Question

How do you know which to pick?

Answer 1

`\boxed{\text{(C)}}`

Step-by-step explanation:

The solid consists of positive and negative ions, so it is an ionic solid.

Ionic solids are brittle, usually water-soluble, and poor thermal conductors as solids. Thus, the correct answer is
`\boxed{\textbf{(C)}}`.

(A) is wrong. It describes a covalent solid, which is soft and always a poor conductor.

(B) is wrong. It describes a covalent solid, which is also low-melting.

(D) is wrong. It describes a metal, and a metal does not contain negative ions.