According to molecular orbital theory, the molecule which contains only $\pi$-bonds between the atoms is

In which of the following changes there is no change in hybridisation of the central atom?

The ratio of lone pair of electrons to bond pair of electrons in ozone molecule is

Identify the number of molecules in which the central atom has one lone pair of electrons from the following list.

$$ \mathrm{PbCl}_2, \mathrm{PH}_3, \mathrm{ClF}_3, \mathrm{SF}_4, \mathrm{BF}_3, \mathrm{SnCl}_2 $$