The formula of a compound represents:

1. an atom
2. a molecule
3. an ion
4. all of these

Which of the following sets of elements show variable valencies?

1. Iron and calcium
2. Copper and sodium
3. Lead and mercury
4. Silver and potassium

Which of the following has zero valency?

1. Hydrogen
2. Chlorine
3. Carbon
4. Neon

The valencies shown by copper is:

1. 1 and 2
2. 2 and 3
3. 2 and 4
4. 1 and 3