Do all molecules contain only single bonds

The given statement is false.

Explanation:

A single bond is defined as the bond through which two same or different atoms are combined to each other by a single line. It is represented by a hyphen.

For example, C-H shows that both carbon and hydrogen atoms are attached to each other through single bond.

It is not necessary that all the molecules contain a single bond. This is because there are molecules which contain a double or triple bond also.

For example, is ethene molecule and it contains a double bond.

Therefore, we can conclude that the statement all molecules contain only single bond, is false.