Hydrogen Bonding

Hydrogen bonding occurs in molecules where hydrogen is bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine. Dimethyl ether does not exhibit hydrogen bonding because the hydrogen atoms are not directly bonded to an electronegative atom.

In the formation of the ammonium ion ( ), the nitrogen atom in shares its lone pair of electrons with a hydrogen ion (H ), which does not have any electrons.
This forms a co-ordinate (dative) bond.
In this bond, both electrons are provided by the nitrogen atom of the ammonia molecule, making it a co-ordinate bond.

Thus, the correct answer is (c).