If we leave a piece of iron in the open for some time, it acquires a coating of brownish substances. This substance is called rust and the process of its formation is called rusting. This is the change that effects iron articles and slowly destroys them. Since iron is used in making bridges, ships, cars, truck bodies and many other articles. The monetary loss due to rusting is huge. For rusting the presence of both oxygen and water (or water vapour) is essential. Infact, if the moisture content in air is high which means if it is more humid, rusting becomes faster.
Methods of preventing rust formation: Rusting of an iron object can be prevented or reduced by not allowing air and moisture to come in contact with the surface of iron objects. Following are the methods of prevention form rusting.
(i) Putting oil or paint over the surface of iron implements.
(ii) Galvanization: In this method, surface of iron is covered with a layer of more active metal like zinc. Zinc metal looses electrons in preference to iron and hence, prevents the rusting of iron.
(iii) By tin-plating 
(iv) Use of anti-rust solutions: Alkaline chromate and alkaline phosphate solution act as anti-rust solutions. When iron objects are dipped into a boiling and strongly alkaline solution of sodium phosphate, a protective insoluble film of iron phosphate is formed on them. This film protects the article form rusting.

(a) The given figure is of ginger tuber.
(b) Asexual reproduction is seen in this plant.
(c) Ginger is a stem.
(d) Various parts of this plant can be shown as follows:

The method of seed dispersal in the fruits and the parts which help in the seed dispersal:

When the reproduction in an organism includes two types of gametes, i.e male and female from two different parents, it is called sexual reproduction, The sexual reproduction takes place by the fusion of male and female gametes by the process called fertilisation to form zygote.

Sexual reproduction (fertilisation) in plants The different steps that take place during sexual reproduction in plants are
(i) The pollens are deposited on stigma and begin to germinate.
(ii) Pollen tube containing male gametes reaches to the ovary of flower.
(iii) The tip of the pollen tubes gets dissolved and male gametes comes out of the pollen tube.
(iv) Inside the ovary male gametes fuse with the female gamete or egg present in the ovule.
(v) The fusion of both the gametes will result into a fertilised egg cell which is also called as zygote.

(a) Figure A indicates inhalation and figure B indicates exhalation.
(b) Movement of air, diaphragm and ribs are indicated in below figure

(a) Exhalation process of respiration is being tested in the activity.
(b) The lime water in test tube B turns milky but water in test tube A remains unchanqed Because CO₂ is present in the exhaled air, it mixes with lime water in test tube B and turns it milky.

(a) Yes, rust is iron oxide (Fe₂O₃). Thus, rust and iron are not the same substance.
(b) No, rusting of iron is a chemical change because in this reaction, a new substance, rust (iron oxide) is formed. It cannot be reversed by any method.
(c) Yes, rusting of iron is a chemical change. During the rusting of iron, it combines with the oxygen in the presence of water (moisture) to form a new compound 'iron oxide'. This iron oxide is a rust.
Iron + Oxygen + Water \(\longrightarrow\) Iron oxide
(From damp air)                    (Rust)
It is a permanent change which cannot be reversed back. So, rusting of iron is a chemical change.
(d) Two other examples are
(i) Setting of curd from milk.
(ii) Burning of magnesium ribbon to form magnesium oxide.

Strong wind and rain can cause soil erosion from the barren land. This can be shown by performing an activity.
Take a wooden block and place some soil or sand on it. Keep an ice-cube tray at one end of the wooden black. Take a small battery-operated fan or hair dryer and hold it at the other end of the black near sand so that it blows the sand into the tray.
We will observe that when the fan blows it causes sand or soil particles to move and these get land in the various compartment of the ice-cube tray. This activity shows that the wind blows the soil on a barren land and may cause soil erosion.

(a) Evergreen rainforest with the greatest variety of plants are seen in equational region.
(b) In tropical regions, vegetation varies from broad leaves evergreen trees to tropical deciduous trees to grassland.
(c) The plants in the arid of desert regions have modified leaves covered with hair or waxy coating and an extensive root system.
(d) Conifers are maintained and adapted to withst and snow fall and shortage ofwater in colder belt.
(e) Anand is observant and sincere boy. He is not afraid to ask question in the class.

We should eat freshly cut apple because if we leave the apple after cutting, it starts turn to brownish due to the oxidation of the essential nutrients present in it and its food value decreases.

The two methods to prevent rusting are
(i) Painting the iron articles.
(ii) Greasing or oiling the iron articles.

Metals like chromium and nickel are mixed (alloyed) with iron to make stainless steel.

Zinc metal is used for galvanising iron.

The common salt can be obtained by the evaporation of sea water.

Magnesium oxide is basic in nature because it turns red litmus solution to blue.

Ca (OH₂)           +          CO₂              \(\longrightarrow\)        CaCO₃         +       H₂O
Calcium hydroxide   Carbon dioxide             Calcium carbonate    Water

Souring of milk is a chemical change because original substances present in milk lose their nature and identity and form new chemical substances.

Ripening of a fruit is a chemical change because after ripening, a new product with different properties is formed.

When magnesium is burnt in the air then a brilliant white flame is obtained.

(i) Curdling of milk, chemical change.
(ii) This change is done by Lactobacillus bacteria and it is beneficial/useful for us.
(iii) By converting lactose sugar into lactic acid.
(iv) Irresponsibility, carelessness

These are chemical changes :
Magnesium + Oxygen⟶ Magnesium oxide
Magnesium oxide + Water ⟶ Magnesium hydroxide

Dissolving of the ash in water is a chemical change.
Reason: When magnesium is burnt in air, it forms magnesium oxide in the form of white ash. 
Mg + O₂ ⟶ MgO (magnesium oxide)

(a) Stainless steel is an alloy of iron mixed with certain corrosion resistant non-metal.
(b) It is a physical change.
(c)The coating of zinc protects iron pipes from the effects of air and moisture and thus does not r

Differences between ice, water and steam:

Difference between physical and chemical changes.

Yes, electric current have other effect except heating, i.e. magnetic effect of current.
When electric current is passed through a coil, there is a magnetic field developed around the coil or wire, if magnetic compass is placed near by, it deflects the magnetic needle.

Since the magnetic effect directly depends on the number of turns of the coil. As, Paheli's coil has more number of turns than Boojho. So, her electromagnet is stronger than Boojho.
So, electromagnet of Paheli attracts more pins as compared to Boojho.

Difference between an open circuit and a closed circuit

As we know that a battery is a combination of two or more cells and it can be constructed by placing cells property on cell holder in such a way that the positive terminal of one cell is connected to the negative terminal of other.
A piece of wire is connected to each of the two metal clips on the cells holder.

If cells are placed side by side, then with the help of some connecting wires, the positive terminal of one cell is connected to the negative terminal of other to produce a combined power of all cells which can be called a battery.

No, we cannot use same fuse in a geyser and in a television set because the fuse used in every appliances has some limit to withstand the current flows through it. So, different appliances have different fuses.