The crystal of Silver Iodide(AgI) shows anisotrpy in coefficient of thermal expansion which means, _____.

positive in one direction and negative in another direction

The correct answer is 2. positive in one direction and negative in another direction.

Anisotropy in coefficient of thermal expansion means that the crystal expands at different rates in different directions. In the case of silver iodide, it expands in the c-direction (along the crystallographic axis) but contracts in the a-direction (perpendicular to the c-direction).

This is due to the different bonding arrangements in the crystal. In the c-direction, the silver and iodine atoms are bonded together in a linear chain. This chain is very strong and it does not expand much when heated. In the a-direction, the silver and iodine atoms are bonded together in a square planar arrangement. This arrangement is weaker than the linear chain and it expands more when heated.

The anisotropy in coefficient of thermal expansion of silver iodide can have important implications for its properties. For example, it can make the crystal more susceptible to cracking and breakage when heated.