The number of $Cl=O$ bonds in perchloric acid is:

Which of the following consists of an equal number of $p\pi - p\pi$ and $p\pi - d\pi$ bonds?

Number of electron-deficient molecules among the following $PH_{3}$,$B_{2}H_{6}$,$CCl_{4}$,$NH_{3}$,$LiH$,and $BCl_{3}$ is ..... .

How many lone pairs of electrons are present in a hydroxyl ion?

Fill in the blanks given below:
$(i)$ The two theories based on the principles of quantum mechanics are ........ and ......... .
$(ii)$ The electronic configuration of carbon in the excited state is ........... .
$(iii)$ Through the combination of atomic orbitals,....... are formed.
$(iv)$ The ${\rm{CH}}_4$ molecule has a .......... shape.

Which of the following species contains four lone pairs of electrons?