The correct order of $K_a$ in aqueous solution at $298 \ K$ for the hydrides of group $16$ elements is:

What is $Oleum$?

Among the following allotropic forms of sulphur,the number of allotropic forms,which will show paramagnetism is ..... .
$(A)$ $\alpha$-sulphur
$(B)$ $\beta$-sulphur
$(C)$ $S_2$-form

Which of the following dinegative anions is quite common?

Which of the following oxides is $\underline{\text{NOT}}$ volatile?

Identify the correct statements from the following:
$i$. Sulphuric acid is manufactured by contact process.
$ii$. $SO_3$ dissolves in $H_2SO_4$ to form pyrosulphuric acid $(H_2S_2O_7)$.
$iii$. $H_2SO_4$ is used in the manufacture of fertilisers such as ammonium sulphate and super phosphate.
$iv$. In the reaction,$S + 2H_2SO_4 (\text{conc.}) \longrightarrow 3SO_2 + 2H_2O$,$H_2SO_4$ is oxidised to $SO_2$.