The strongest reducing agent among the following is:

On heating ammonium dichromate,the gas evolved is

When phosphine is passed through an aqueous solution of copper sulphate,the product produced is:

Strong reducing behaviour of $H_3PO_2$ is due to

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?

The basicity of orthophosphoric acid $(H_3PO_4)$ is: