Define physical change and chemical change. state which type of change occur in each of the following statemenet:
(a) passing an electric current through molten magnesium chloride yields moltenm magnesium and gaseous chlorine.
(b) the iron in discarded automobiles slowly forms reddish brown, crumbly rust.

Physical change: It is reversible process and we can get back to orginal material. Best example is the interconversion of ice into water which inturn into vapour.

Chemical changes are irreversible and we can't get back the original material. Example combustion of coal, rusting of iron

Explanation:

1. Electrolysis of molten MgCl2 is chemical change since we can't get back MgCl2 after Electrolysis and new materials are formed.

2. It is an example rusting of iron comes under chemical changes.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.