(i) A combination reaction is a reaction in which two or more reactants combine to form a compound.
(ii) It is also called as synthesis reaction (or) composition reaction (a single product).
(iii) S_(s) + O_2(g) → SO_2(g)
(iv) Sulphur reacts with oxygen it produce sulphur dioxide.
(v) Most of combination reactions are exothermic in nature, because they involve the formation of new bonds, which releases a huge amount of energy in the form of heat.

Deliquescent	Hygroscopic
Copper sulphate pentahydrate, Calcium chloride, Gypsum Salt.	Conc. Sulphuric acid, Silica gel.

(i) Aqueous solution:
a) The solution in which water acts as a solvent is called aqueous solution.
b) Example: common salt in water, Copper Sulphate in water.
(ii) Non - Aqueous solution:
a) The solution in which any liquid, other than water, acts as a solvent is called non-aqueous solution.
b) Example: Sulphur dissolved in carbon disulphide, Iodine dissolved in carbon tetrachloride

(i) Melting point of tungsten is very.
(ii) Hence it is used in a filament bulb.
(iii) But a fuse wire should be made up of material which has low melting point.

Hydrogen chloride (HCl), Hydrogen iodide (HI) are two examples for heterodiatomic molecules.

S. No	Mass	Weight
(i)	Fundamental quantity.	Derived quantity.
(ii)	It is the amount of matter containing in a body.	It is the gravitational pull acting on the body.
(iii)	Its unit is kilogram (kg).	Its unit is newton (N).
(iv)	Remains the same.	Varies from one place to another place.
(v)	It is a scalar quantity.	It is a vector quantity.

Given: Length, L = 10 m
Resistance, R = 2 ohm
Area, A = 2 × 10^–7 m²
Resistivity, ρ = \(\frac{RA}{L}\)= \(\frac{2 \times 2 \times 10^{-7}}{10}\)
= 4 × 10^–8 Ω m
Conductance, G = \(\frac{1}{R}=\frac{1}{2}\) = 0.5 mho
Conductivity, σ = \(\frac{1}{ρ}\)= \(\frac{1}{4 \times 10^{-8}}\)
= 0.25 × 10⁸ mho m^–1

(i)  Mass percentage of the solute
Mass percentage of solute = \(\begin{aligned} & \frac{\text { Mass of the solute }}{\text { Mass of the solute +Mass of the solvent}} \times 100 \\ \end{aligned}\)
= \(\frac{16 × 100}{16 + 100}\)
\(=\frac{1600}{116}\)
Mass percentage of the solute = 13.79 %
(ii) Mass percentage of solvent = 100 - (Mass percentage of the solute)
= 100 – 13.79
= 86.21%

A) Since the resistors are connected in parallel, the potential difference across each resistor is same (i.e. V=10V)
Therefore, the current through R₁ is,
\({ I }_{ 1 }=\frac { V }{ { R }_{ 1 } } =\frac { 10 }{ 5 } =2A\)
Current through \({ R }_{ 2 }={ I }_{ 2 }=\frac { V }{ { R }_{ 2 } } =\frac { 10 }{ 10 } =1A\)
Current through \({ R }_{ 3 }={ I }_{ 3 }=\frac { V }{ { R }_{ 3 } } =\frac { 10 }{ 20 } =0.5A\)
B) Total current in the circuit, I = I₁ + I₂ + I₃
= 2 + 1 + 0.5 = 3.5 A
C) Total resistance in the circuit  \(\frac { 1 }{ { R }_{ P } } =\frac { 1 }{ { R }_{ 1 } } +\frac { 1 }{ { R }_{ 2 } } +\frac { 1 }{ { R }_{ 3 } } \)
\(=\frac { 1 }{ 5 } +\frac { 1 }{ 10 } +\frac { 1 }{ 20 } \)
\(=\frac { 4+2+1 }{ 20 } \)
\(\frac { 1 }{ { R }_{ P } } =\frac { 7 }{ 20 } \)
Hence, \({ R }_{ P }=\frac { 20 }{ 7 } =2.857\Omega \) 

Data:
Level of the liquid L₁ = 50 ml
Level of the liquid L₂ = 48.5 ml
Level of the liquid L₃ = 51.2 ml
Apparent expansion = L₃ − L₁
= 51.2 ml – 50 ml = 1.2ml
Real expansion = L₃ − L₂
= 51.2 ml – 48.5ml = 2.7ml
So, Real expansion > apparent expansion

Given \(\mathrm{m}=1 \mathrm{~kg}, \quad \mathrm{v}=10 \mathrm{~m} \mathrm{~s}^{-1}\)
When a ball bounces back with the same speed, the momentum changes from mv to -mv. So, the change in momentum is -2 mv.
Δp = mv - mu
= -mv - mv
\(=-2 \mathrm{mv}=-2 \times 1 \times 10 \)      \([Here \ mu = mv \\ mv = -mv]\)
\(\therefore \Delta P=-20 \mathrm{~kg} \mathrm{~m} \mathrm{~s}^{-1}\)

Deliquescence substances	Hygroscopic substances
When exposed to the atmosphere at ordinary temperature, they absorb moisture and do not dissolve.	When exposed to the atmospheric air at ordinary temperature, they absorb moisture and dissolve.
Hygroscopic substances do not change its physical state on exposure to air.	Deliquescent substances change its physical state on exposure to air.
Hygroscopic substances may be amorphous solids or liquids.	Deliquescent substances are crystalline solids.
Hygroscopic substances are used as drying agents.	Deliquescent Substances are not used as drying agent.
Example : H2SO4.P2O5	Example : NaOH, KOH

Important factors that affect rate of a reaction are:
(i) Nature of the reactants
(ii) Concentration of the reactants
(iii) Temperature
(iv) Catalyst
(v) Pressure
(vi) Surface area of the reactants
(i) Nature of the reactants:
a) The reaction of sodium with hydrochloric acid is faster than that with acetic acid.
b) Because Hydrochloric acid is a stronger acid than acetic acid and thus more reactive.
c) \(2 \mathrm{Na}_{(\mathrm{s})}+2 \mathrm{CH}_{3} \mathrm{COOH}_{\text {(aq) }} \rightarrow 2 \mathrm{CH}_{3} \mathrm{COONa}_{\text {(aq) }}+\mathrm{H}_{2(\mathrm{~g})} \rightarrow (slow)\)
d) 2 Na_(S)+ 2HCI_(aq) ⟶ 2NaCI_(aq)+ H_2(g) ⟶ fast
(ii) Concentration of the reactants:
a) The amount of the substance present in a certain volume of the solution is called 'concentration'.
b) More the concentration, more particles per volume exist in it and faster the reaction.
c) Granulated zinc reacts faster with 2 M hydrochloric acid than 1 M hydrochloric acid.
(iii) Temperature:
a) Most of the reactions go faster at higher temperature.
b) Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction.
c) E.g: Calcium carbonate reacts slowly with hydrochloric acid at room temperature and faster when temperature increases.
(iv) Pressure:
a) Increasing the pressure of reactant gases increases the reaction rate.
b) Because, increasing pressure the reacting particles come closer and collide frequently.
(v) Catalyst:
a) A catalyst is a substance which increases the reaction rate without being consumed in the reaction.
b) E.g: On heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate.
c) If manganese dioxide is added, it increases the reaction rate.
(vi) Surface area of the reactants:
a) When solid reactants are involved in a reaction, their powdered form reacts more readily.
b) Because, powdering of the reactants increases the surface area and more energy is available on collision of the reactant particles.
c) Thus, the reaction rate is increased.
d) E.g: Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips.

a) Ultrasonic Vibrations:
(i) The Vibrations produced by sound waves with a frequency greater than 20 KHz are called ultrasonic vibrations.
(ii) Human ear cannot detect these waves.
b) Uses of Ultrasonic vibration:
(i) Ultrasonic devices are used to detect objects and measure distances.
(ii) Ultrasound imaging or sonography is often used in medicine.
(iii) In the non destructive testing of products and structures. Ultra sound is used to detect invisible flaws.
c) Certain creatures like mosquitoes, dogs, bats and dolphins can detect these waves.

a) Electric current:
(i) Electric current is often termed as 'current' and it is represented by the symbol 'I'.
(ii) It is defined as the rate of flow of charges in a conductor.
(iii) This means that the electric current represents the amount of charges flowing in any cross-section of a conductor (say a metal wire) in unit time.
(iv) If a net charge 'Q' passes through any cross-section of a conductor in time 't', then the current flowing through the conductor is
\(I=\frac{Q}{t}\)
b) SI unit of electric current:
(i) The SI unit of electric current is ampere (A).
(iii) The current flowing through a conductor is said to be one ampere, when a charge of one coulomb flows across any cross-section of a conductor, in one second. Hence,
\(1 \text { ampere }=\frac{1 \text { coulomb }}{1 \text { second }}\)
c) Ammeter is used to measure the electric current. It should be connected in series in a circuit.

(i) Propulsion of rockets is based on law of conservation of linear momentum as well as Newton's III law of motion.
(ii) Rockets are filled with a fuel (either liquid or solid) in the propellant tank.
(iii) When the rocket is fired, this fuel is burnt and a hot gas is ejected with high speed from the back nozzle producing a huge momentum.
(iv) To balance this momentum, an equal and opposite reaction force is produced combustion chamber which makes the rocket project forward.
(v) While in motion, the mass of the rocket gradually decreases, until the fuel is completely burnt out.
(vi) Since there is no net external force acting on it, the linear momentum of the system is conserved.
(vii) The mass of the rocket decreases with altitude, which results in the gradual increase in velocity of the rocket.
(viii) At one stage, it reaches a velocity, which is sufficient to just escape from the gravitational pull of the Earth. This velocity is called escape velocity.