The green colour of ferrous sulphate crystals is due to the presence of 7 water molecules (water of crystallization). :It loses the water of crystallization on heating, thus leading to change in colour.

The blue colour of copper sulphate is due to its crystalline nature which holds 5 water molecules (water of crystallization). On heating, the water molecules disappear and anhydrous copper sulphate (white in colour) is left back.

Exothermic reaction: Beaker A, Beaker B.
Endothermic reaction: Beaker C, Beaker D.

Arnav had already reacted Mg with dil. HCI to form MgCl₂ and gas. The piece of metal that Deepak used was not magnesium but magnesium chloride (MgCl₂), hence it did not react with the given acids.

Red litmus turned blue.
Blue litmus remained blue.
This is because the magnesium ribbon on burning in air, forms the white magnesium oxide. When this is dissolved in water, it forms magnesium hydroxide, which is basic in nature.

Advantage: In some metals a protective layer is formed on its surface to prevent it from further corrosion.
E.g., aluminium (Al) forms a layer of Aluminium oxide (Al₂O₃) by corrosion. The layer prevents further corrosion.
Disadvantage: Loss of the metal.

(a) It is the path of light.
(b) Group of parallel light rays emitted by the source of light.
(c) Bouncing back of light after striking any surface.
(d) The surface which reflects the light.
(e) The distance between the pole and the principal focus of the spherical mirror.
(f) A point of the principal axis where the rays of light parallel to principal axis meet.
(g) Bending of light ray when it travels from one medium to another.
(h) When the speed of light is more as compared to other medium.
(i) When the speed of light is less as compared to another medium.
(j) The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power
(k) It is the power of lens whose focal length is 1 m.

Male individual has 23 pairs of chromosomes but the gamete that is formed by the meiotic cell division contain only half the number of chromosomes i.e., 23 chromosomes in male sperm and 23 chromosomes in female egg. It is the fusion of this sperm and egg which leads to an offspring with 23 pairs of chromosomes.

(i) The differences can be due to inheritance of acquired traits. When respective parents are different from each other the variation occurs due to inheritance.
(ii) Body design.

If magnification is 1, the image size is same as that of object size.
Since, magnification is positive, the image is erect and virtual.