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.

Which of the following elements has atomicity 4?

1. Iodine
2. Ozone
3. Phosphorus
4. Sulphur

A molecule is the smallest unit of :

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