The element which does not belong to group $15$ is

Why is dioxygen a gas but sulphur a solid?

Explain the nature of oxides of group-$16$ elements. Write a note on halide compounds of group-$16$ elements. Write a note on hydride compounds of group-$16$ elements.

How many total statements are correct in the following?
$(i)$ $SO_2$ - antichlor,preservative
$(ii)$ $O_3$ - Disinfectant
$(iii)$ $Cl_2$ - Antiseptic
$(iv)$ $O_2$ - used in oxy-acetylene welding
$(v)$ $PH_3$ - used in smoke screens
$(vi)$ $HNO_3$ - Pickling of stainless steel

Which of the following is not correct?

Which of the following is the structure of oleum?