X. Sodium bicarbonate (NaHCO₃)

 C₂H₆C₃H₆

(i) Fresh milk is acidic and can spoil easily. In presence of baking soda, milk becomes alkaline and can be stored for a longer time.
(ii) When milk is set to curd, its pH decreases. The alkali does not allow it to become more acidic easily. So it will take more time

Balanced Equation
\(2{ FeSO }_{ 4 }\overset { Heat }{ \rightarrow } { Fe }_{ 2 }{ O }_{ 3 }(s)+S{ O }_{ 2 }(g)+{ SO }_{ 3 }(g)\)

They get tarnished by reacting with atmospheric air to form silver sulphide.

Given, Resistance, R = 8 \(\Omega\) , Current, J = 15 A
Time, t = 2 h = 7200 s
\(\therefore\) Heat developed. H = J²Rr
=15 \(\times\)15 \(\times\) 8 \(\times\) 7200 J
\(\therefore\) Rate of heat developed.
\(P=\frac{H}{t}=\frac{15\times 15\times 8 \times 7200}{7200}\)
= 1800 W or 1800J/s
Thus, the rate at which heat is developed in the heater is 1800 joule per second.

(a) Alkali metals are soft and reactive. For example Na, K etc.,
(b) Limestone is calcium carbonate, therefore, the important constituent of limestone is calcium.
(c) Metals which exist in the liquid state at room temperature are mercury (Hg) and francium (Fr)

(i) -COOH (Carboxylic acid)
(ii) -CHO (Aldehyde)

(i) (-Cl) Halogen (Chloro)
(ii) -OH) Alcohol

The processes that together perform the maintenance functions of living organisms are called life processes.

The phenomenon in which an electric current is induced in a circuit because of a changing magnetic field is called electromagnetic induction.

When the total current drawn by all the appliances at a particular time exceeds the bearing capacity of that wire, the wires of the domestic wiring gets heated. This is called overloading.

Solder is an alloy of lead and tin.

Oxides ores, carbonate and sulphide ore.

The blood vessels which carry blood from organs to the heart are veins.

Breathing is the process of taking in oxygen (inhalation) and giving out carbon dioxide (exhalation)

The heat energy obtained in the form of steam from under the earth's crust is called geothermal energy.

Shoot of the plant bends towards light due to phototropism. The stimulus is light and the movements of shoot is towards light.

Fore brain

Pancreas. It secretes hormones and digestive enzymes.

Hind brain

Coulomb

Watt

In a domestic circuit, parallel connection of devices is preferable for several reasons:
a. In series connection, if one of the devices is defective, if one of the devices is defective,     then the current of the entire circuit is cut off. As a result, all the devices stop working. In parallel connection, even if one device is defective, the others continue working.
b. In series connection, selective operation of devices is not possible, but this is not so in the case of parallel connection.
c. In series connection, the same current passes through all the devices, regardless of the fact that different devices require different values of current to operate. In parallel connection, different values of current can be obtained for different devices according to their requirements.

The bronchi, within the lungs divide into smaller tubes called bronchioles and finally terminate in balloon-like structures called 'alveoli'. The alveoli are made up of thin moist membranes which are richly supplied with blood and provide a very large surface area for the gaseous exchange.

Metals present at the bottom of the reactivity series do not corrode easily, e.g. gold, silver, platinum etc.

Precipitation reaction

Heat, light and electricity.

A solution of ammonia in water results in the formation of ammonium hydroxide (NH₄OH).  Ammonium hydroxide is basic in nature and turns red litmus blue.

A represents an acid solution.  This is because the pH value of A is 2.0 and the pH value of an acids lies between 1 and 6.

The colour of copper sulphate solution changes when an iron nail is dipped in it because iron being more reactive than copper, displaces copper metal from aqueous copper sulphate solution. Thus, blue colour of copper sulphate fades away to give green colour solution of ferrous sulphate.
Fe (s) + CuSO₄(aq) \(\rightarrow\) FeSO₄(aq) + Cu(s)
Grey       Blue                  Green         Brown       

i) Since compound C on combustion forms two moles of CO₂ and 3 moles of H₂ O, therefore compound C must contain two carbon atoms and six hydrogen atmos. Thus compound C must be C₂H₆ (ethane)
\(\underset{Ethene(C)}{2C_2H_6}+\underset{Oxygen}{7O_2}\xrightarrow{Heat}\underset{Carbon\ dioxide}{4CO_2}+\underset{Water}{6H_2O}\)
ii) Since compound (C) is obtained by addition of 1 mole of H₂ in presence of Ni to compound (B), therefore (B) must be ethane.
\(\underset{Ethene(B)}{CH2}=CH_2+H_2\xrightarrow{Ni/Heat}\underset{Ethene(C)}{CH_3-CH_3}\)
iii) Since compound (B) is formed by heating compound (A) with cone. H₂SO₄ therefore compound (A) must be ethanol.
\(\underset{Ethanol(A)}{CH_3CH_2OH}\xrightarrow{Conc. H_2SO_4,443K}CH_2=CH_2+\underset{Ethene(B)}{H_2O}\)

(i) An alloy is a homogenous mixture of two or more metals. It sometimes contains a non -metal component also.
(ii) It is made by heating the components in a definite proportion and then uniformly mixing them in the molten state and then cooling.
(iii) Two purposes of making alloys are:
     (a) To make a substance resistant to corrosion
     (b) To make a substance strong and hard
(iv) Constituents of Stainless steel:
     Iron, nickel, and chromium
(v) Two properties of stainless steel are:
     (a) It is resistant to corrosion.
     (b) It is more durable.
(vi) Constituents of Brass:
      Copper and Zinc
(vii) Two properties of brass are:
       (a) It is resistant to corrosion.
      (b) It is more malleable.

Food is prepared in the green leaves of the plant by combining carbon dioxide and water in presence of sunlight and chlorophyll. The carbon dioxide required for photosynthesis is taken by the plants from air. The carbon dioxide enters the leaves through tiny pores called stomata. The water required is taken from soil. The sunlight provides the energy required to carry out the preparation of food. The green pigment called chlorophyll present in green leaves help to absorb energy from sunlight. The oxygen produced as a by-product goes into the air.
The food prepared by the green leaves is in the form of glucose. This glucose is sent to different parts of the plant. The excess glucose is changed into starch and is stored in the leaves of the plant. The food prepared by photosynthesis provides all the energy to a plant which it needs to grow. Thus, it is clear that the green plants convert sunlight energy into chemical energy. by making food. When we eat plant foods such as fruits, vegetables, food grains etc., the chemical energy stored in them is released in our body during respiration.
During the process of photosynthesis, the following three steps take place:
(i) Absorption of sunlight energy by chlorophyll.
(ii) Conversion of sunlight energy into chemical energy and splitting of water into hydrogen and oxygen using sunlight energy.
(iii) Reduction of carbon dioxide to form carbohydrates using the chemical energy.

The Substance which is used for making different shapes is Plaster of Paris.  Its chemical name is calcium sulphate hemihydrate \([CaSO_4.1/2H_2O].\) The two formula unit of \(CaSO_4\) share one molecule of water.  As a result, it is soft.  When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.

\(\underset{Plaster\ of\ Paris}{​​CaSO_4.{1\over 2}H_2O}+1{1\over2}{H_2O}\rightarrow \underset{Gypsum}{CaSO_4.2H_2O}\)

(a) Carbon dioxide turns lime water milky as it forms calcium carbonate with lime water. This is the characteristics test for carbon dioxide.
Ca(OH)₂ + CO₂ --> CaCO₃ + H₂O
(b) The smell of sulphur dioxide gas is like burning of sulphur, which is the characteristics test for sulphur dioxide. Sulphur dioxide turns moist litmus paper from blue to red.
(c) When a burnt candle or match stick is brought near the oxygen gas, it starts burning brightly. This is the characteristic test for oxygen gas.
(d) When a burnt candle or match stick is brought near the hydrogen gas, it burns with pop sound, which is the characteristic test for hydrogen gas.

(i) Before heating, it is pale green.
After heating, it is brown or reddish brown.
Two observations are:
(a) Change in state and colour
(b) Evolution of gas
(ii) Decomposition reaction
2FeSO₄(s) \(\overset { Heat }{ \rightarrow } \) Fe₂O₃(s) + S0₂(g) + SO₃(g) 

(i) The gas evolved is hydrogen.
(ii) Zn(s)+H₂SO₄(aq)\(\rightarrow\)ZnSO₄(aq)+H₂\(\uparrow\)
Test for H₂ gas: The presence of H₂ gas can be tested by passing the gas through soap solution and then bringing a burning splinter near the soap bubbles filled with the gas. If the gas burns with a pop sound, it is hydrogen.

(i) X - Carbon, Y - Diamond, Z - Graphite
(ii) Non-metal
(iii) Tin.

(i) Gold and silver are most malleable metal and most ductile metal,
(ii) Silver is the best conductor of heat and lead is the poorest conductor of heat.
(iii) Metal with highest melting point - Tungsten, iron. Metal with lowest melting point - Gallium, Cesium.

(i) Alkali. e.g., NaOH (Sodium hydroxide).
(ii) Tooth decay starts when the pH of the mouth is lower than 5·5.It can be prevented by using tooth pastes which are generally basic.
(iii) Bee-sting has acid that causes pain and irritation. Baking soda is alkaline, neutralises the acid and gives relief.

The major differences between an electric motor and generator are stated below:
Electric Motor:
1. It converts electrical energy into mechanical energy.
2. It needs electrical energy for its works.
3. They are used as water pumps, marble grinders etc.
Generator:
1. It converts mechanical energy into electrical energy
2. It needs mechanical energy for its working.
3. They are used as water pumps, marble grinders etc.
4. diesel generator, hydro-electric generator are the examples of it.

Breathing is the process by which oxygen is taken in (inhalation) and carbon dioxide is released out (exhalation). Respiration involves the oxidation of the food we eat to release energy. Carbon dioxide produced as a result of this is released out during exhalation.
Aerobic respiration: During aerobic respiration, the oxidation of food takes place in the presence of oxygen. Aerobic respiration can be summarised by the given equation:
\({ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }+{ 6O }_{ 2 }\longrightarrow { 6CO }_{ 2 }+{ 6H }_{ 2 }O+Energy\)
Anaerobic respiration: During anaerobic respiration, food is broken down in the absence of oxygen. It is also known as fermentation and is more common in microorganisms such as yeast.
Sometimes pyruvate gets converted into lactic acid in muscles by the process of anaerobic respiration.
\({ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }\xrightarrow [ ]{ Absenceofoxygen } Alcohol+{ CO }_{ 2 }+{ H }_{ 2 }O+Energy\)

(i)Bile is helpful in the emulsification of fats i.e., the breaking down of large fat droplets into smaller fat globules, which the pancreatic enzymes can act upon.
(ii)The pancreatic juice contains enzymes that require an alkaline medium to act. The bicarbonate secreted by the duodenum provides this alkaline medium.
(iii)The function of pancreatic amylase is to convert complex carbohydrates into glucose, which is absorbed in the blood.

(a) The solar cooker box is covered with a plane glass plate so as to prevent heat from escaping.
(b) Sun is said to be the ultimate and the original source for most of the energy present on the earth. When sun rays fall on oceans and other water bodies, the water present in the water bodies gets evaporated and rises up in the atmosphere. In the upper part of the atmosphere, this water vapour gets condensed and forms douds, which give rain on the high lands. Therefore, the rain water runs over the Sand surface towards the large water bodies. This running water over the land surfaces is called river. Therefore, the energy of running water actually originates from the solar energy. This is why solar energy of water flowing in a river is considered to be an indirect form of solar energy.
(c) The fission of nucleus is brought about by splitting the nucleus of heavy atoms, such as uranium or plutonium, with low-energy neutron bombardment. 

(a) A solar cell is a device which converts solar energy into electricity. It is a sandwich of a silicon-boron layer and a silicon-arsenic layer.
(b) Biogas is an ideal fuel for domestic use because it is a cheap and clean fuel, which does not leave behind any residue.
(c) A nuclear power plant is a device in which controlled chain reaction is used.

Information passes through neuron in the form of electro-chemical signals. These signals are called impulse.
When an impulse reaches the end of the axon it sets off the release of some chemicals. These chemicals cross the gap or the synapse and start a similar electrical impulse in a dendrite of the next neuron. A similar synapse allows the delivery of impulses from the neurons to other cells, like muscle cells or glands.

It is given that: Voltage (V) = 2.50 V
Current (I) = 750 mA = 0.75 A
The bulb is lighted for 4 hours.
Thus,
(i) Power generated (P) = VI = 2.50\(\times\) 0.75 = 1.87 W
(ii) Resistance (R) = \(\frac { V }{ I } =\frac { 2.5 }{ 0.75 } =3.33\Omega \)
(iii) Energy consumed in 4 hours = Power\(\times\)Time = P\(\times\)t =1.87\(\times\)4 = 7.48  Wh

(i) A and B belong to group 1 and 2 because they form basic oxides. C belongs to group 13 as it has 3 valence electrons. D belongs to group 14 as it forms almost neutral oxide. E and F belong to group 15 and 16 as they form acidic oxides. G belongs to group 17 as it has 7 valence electrons and H belongs to group 18. They belong to 3rd period of Periodic Table because sodium belongs to 3rd period and AG is NaCl, ionic compound of sodium which can be obtained from sea water and A(Na) and G( Cl) belong to 3rd period.
(ii) H belong to noble gas.
(iii) A has the largest atomic radius.
(iv) E and F are likely to be non-metals.
(v) D is likely to be metalloid or semi-metal.

a) Solar energy can be harnessed by using solar energy devices. These devices either use solar energy directly as heat or convert it into solar energy directly as heat or convert it into electricity. One of the devices is solar cooker.
b) Limitations of solar energy:
i) It is not evenly distributed on the Earth.
ii) It requires costly equipment and infrastructure.
c) Using of solar cells.