(i) Terrestrial planets are the planets that are composed of silicate rocks or metals. It is rocky due to the following reasons:

a. The terrestrial planets were formed in the close vicinity of the parent star where it was warm for the gases to condense to solid particles.

b. The solar winds were most intense near to the sun. So it blew off most of the gas and dust away from the terrestrial planets.

c. Moreover, these planets are small and their lower gravity could not hold the escaping gases.

(ii) a. Kant and Laplace

i. The Nebular hypothesis was firstly given by Kant and later revised by Laplace.

ii. This hypothesis explains the origins and development of the solar system within the framework of naturalism.

iii. According to this hypothesis, the planets were formed out of a cloud of material associated with the sun which was slowly rotating.

iv. It explained that the interior of the earth must be gaseous as the earth had orginated from these gases itself.

b. Chamberlain and Moulton

i. Chamberlain and Moulton's hypothsesis was proposed by Thomas Chamberlian and Forest Moulton.

ii. In 1905, they believed that a wandering star had come closer to the sun.

iii. A cigar shaped extension material was separated from the solar system.

iv. As the passing star moved away. the material separated from the sun and continued to revolve around the sun and eventually formed planets.

(iii) The process of differentiation is explained below:

Differentiation is a process of separating the different elements of a planet due to their physical and chemical behavior.

The body forms different layers. The denser materials sink int the center and the less dense materials rise above.

The different layers of earth, starting from the outside are- crust, mantle, outer core, and inner core.

As we move towards the inner parts of the Earth, the density of the material continues to increase.

(iv) a. The surface of the Earth was barren, rocky and hot.

b. It was covered with a thin atmosphere of hydrogen and helium.

c. It was in the liquid form initially but was late changed to the current state.

(v) The gases which initially formed the earth’s atmosphere were hydrogen and helium.

These gases eventually declined due to the high solar winds.

During the process of Colling of earth, gases and water vapor was released from the interior of the Earth.

This began the process of the current state of the atmosphere.