In the dark,which of the following reacts with hydrogen?

When $KBr$ is treated with conc. $H_2SO_4$,a reddish-brown gas is evolved. The evolved gas is:

When $Cl_2$ is passed through cold dil. $NaOH$,the products are:

Among the following,the number of compounds that can react with $PCl_5$ to give $POCl_3$ is $O_2, CO_2, SO_2, H_2O, H_2SO_4, P_4O_{10}$.

Aluminium trifluoride is insoluble in anhydrous $HF$ but dissolves on addition of $NaF$. Aluminium trifluoride precipitates out of the resulting solution when gaseous $BF_3$ is bubbled through. Give reasons.

Write the names,molecular formulas,and structural formulas of the oxoacids of halogens.