Which of the following is a pair of metalloids ?

1. Na and Mg
2. B and Si
3. C and P
4. He and Ar

Which of the following properties is not shown by compounds ?

1. They are heterogeneous.
2. They are homogeneous.
3. They have definite molecular formulae.
4. They have fixed melting and boiling points.

A molecule is the smallest unit of :

1. an element
2. a compound
3. a mixture
4. an ion

Which of the following substances dissolves in carbon disulphide ?

1. Iron
2. Sulphur
3. Sodium chloride
4. Iron sulphide