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Lone pairs of an electron are added to atoms, such as N and O, which do not always complete their outer shell of electrons through covalent bonds.

So the electron dot structure of caffeine is shown as follows:

Charge cloud means the total number of Lone pairs or bond pairs on an atom. For

${\mathrm{sp}}^3$- 4 charge clouds

${\mathrm{sp}}^2$- 3 charge clouds

$\mathrm{sp}$- 2 charge clouds

Here, in the given structure, all the atoms are surrounded by three charge clouds because all the atoms have a count of three charge clouds (No. of bond pairs or lone pairs).

Hybridization is a concept of mixing atomic orbitals into new hybrid orbitals in an atom and is suitable for the explanation of covalent bond in compounds that do not obey the octet rule.

The hybridization of element A (Carbon atom) is ${\mathrm{sp}}^2$since it involves one s-orbital and two p-orbital.

The hybridization of element B (Nitrogen atom) is ${\mathrm{sp}}^2$ since it involves one s-orbital and two p-orbital.

The hybridization of element C (carbon atom) is ${\mathrm{sp}}^2$since it involves one s-orbital and two p-orbital.