Factors to be considered for fish culture are:
(i) Topography or location of pond.
(ii) Water resources and their quality.
(iii) Soil quality i.e., composition of soil particle size and nutrients present in the soil.

Artificial Insemination
Reason
(i) Semen of bull can be obtained and transported to remote parts of the country. It is because semen can be frozen and can be stored for a long period.
(ii) By artificial insemination many cows (up to 3000) can be fertilized by the semen collected from one bull.

Top soil: The topmost layer of the soil which contains soil particles, humus and living organisms is called top soil.
Two factors are
(i) The average size of soil particles.
(ii) The amount of humus and the microscopic organisms found in it.

Carbon dioxide is fixed in two ways:
(i) Green plants convert carbon dioxide into glucose in the presence of sunlight.
(ii) Many marine animals (like Unio and Pila) use carbonates dissolved in sea-water to make their shells.
This fixation of carbon dioxide keeps its percentage almost constant in the atmosphere.

Atomic mass an element can be obtained by adding the number of protons and neutrons.

An electron revolving in a shell is associated with a definite amount of energy.Its energy changes when it jumps to another shell, that is to say when it goes from one level of energy to another level of energy.Thus a shell also goes the energy of an electron besides its location and are, therefore called energy shells or levels.

The gas in discharged tube experiment (at low pressure and high voltage) get decomposed.Negatively charged particles are produced which travel from cathode to anode, thus facilitating the flow of current.Under other conditions, e.g., 1 atmosphere pressure, no dissociation of gas occurs and no current flows.

1 mole of S₈ = 32 x 8 = 256 g
1 mole of S₈ = 6.023 x 10²³ molecules
256 g S₈ has =  6.023 x 10²³ S₈ molecules
16 g S has = \(\frac { 6.023\times { 10 }^{ 23 } }{ 256 } \times 16=3.76\times { 10 }^{ 22 }\)molecules

Every liquid has a characteristic boiling point at 1 atmospheric pressure. If the given colourless liquid boils at exactly 373K at 1 atmospheric pressure, then it is pure water if the boiling point is even slightly above 373K, then contaminated.

1. Malleability means that metals can be hammered into sheets and foils. For example, aluminium foils are used for wrapping foodstuffs, silver foils are used for decorative purposes on sweet and fruits.
2. Ductility means that metals can be drawn into wire. Gold and silver wires are used in ornaments. Aluminium and copper wires are used for the conduction of electric current.

Mixture of common salt, camphor and iron fillings:
(i) magnet is passed over the mixture several times. Iron fillings attached to one magnet and are separated.
(ii) Camphor is separated from the salt by sublimation. camphor is coollected as sublimate and commonj sali is separated as rsidue.

(i) Simple distillation cannot be used if the boiling point difference between the liquids is less than 20-25⁰ C
(ii) Simple distillation cannot be used if it is a mixture of more than two liquids.

(a) The illumination of the beam of light due to scattering on collision with certain particles is called the Tyndall effect. If a beam of light is passed through a true solution, the solution is not illuminated and light passes unaffected.
(b) (i) Milk,
(iv) starch solution,
(vi) Tincture iodine. In these solutions, the size of particles is larger enough to scatter a beam of light.

Alloy are considered as homogeneous mixture because.
(i) the considered as homogeneous mixtures because
(ii) it shows the properties of its constituent and can have variable composition of its constituents.

The substances are not classified only by their appearances.These are classified by their properties such as density, boiling point or melting point, conductivity, thermal capacity and other chemical properties.sugar and sodium chloride have different physical and chemical properties and so are different substances.