Which of the following elements shows a maximum valency of $5$?

The total number of $\sigma$ and $\pi$-bonds in pyrophosphoric acid are respectively

Pure $HNO_3$ is a colorless liquid,but it turns light brown in the presence of light. This is due to its decomposition into which of the following substances in small amounts?

The correct statement$(s)$ related to oxoacids of phosphorus is(are):
$(A)$ Upon heating,$H_3PO_3$ undergoes disproportionation reaction to produce $H_3PO_4$ and $PH_3$.
$(B)$ While $H_3PO_3$ can act as a reducing agent,$H_3PO_4$ cannot.
$(C)$ $H_3PO_3$ is a monobasic acid.
$(D)$ The $H$ atom of the $P-H$ bond in $H_3PO_3$ is not ionizable in water.

Which of the following nitrogen trihalides is the weakest base?

What happens when a large amount of water is added to a solution of $BiCl_3$?