Which colorless gas has a smell like rotten fish?

The number of $P-O-P$ bridges in the structure of phosphorus pentoxide $(P_4O_{10})$ and phosphorus trioxide $(P_4O_6)$ are respectively:

Which of the following compounds has a $P-P$ bond?

Which gas is used to provide an inert atmosphere?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : $PH_3$ has lower boiling point than $NH_3$.
Reason $(R)$ : In liquid state $NH_3$ molecules are associated through van der Waals forces,but $PH_3$ molecules are associated through hydrogen bonding.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following pairs of oxoacids have a basicity of $2$?