Which of the following ions can exist?

Which of the following forms a dimer by $H$-bond?

Observe the following substances: Ethanol,acetic acid,ethylamine,trimethylamine,salicylic acid,ethanal. In the above list,the number of substances with $H$-bonding is:

When two ice cubes are pressed together,they join to form a single cube. Which of the following forces is responsible for holding them together?

The correct order of the strength of $H$ bonds is

The boiling points of methanol,water,and dimethyl ether are respectively $65\,^{\circ}C$,$100\,^{\circ}C$,and $-24.8\,^{\circ}C$ (note: dimethyl ether is a gas at room temperature). Which of the following best explains these wide variations in boiling point $(b.p.)$?