Which statement is not correct for nitrogen?

In the $15^{th}$ group of the periodic table,the elements $N, P, As, Sb$,and $Bi$ are present. As we move from $N$ to $Bi$,how do the oxides with the general formula change?

Among the hydrides $NH_3, PH_3,$ and $BiH_3$, the hydride with the highest boiling point is $X$ and the hydride with the lowest boiling point is $Y$. What are $X$ and $Y$ respectively?

There is very little difference in acid strength in the series $H_3PO_4$,$H_3PO_3$,and $H_3PO_2$ because

What is the chemical formula of sodium pyrophosphate?

The number of $H$ atoms directly attached to the $P$ atom in hypophosphorous acid is: