(a)[1]
Pick, from the options given, the gas that aquatic life needs: argon, hydrogen, nitrogen, oxygen.
(b)[1]
Match each harmful substance in the left-hand column with the correct effect on the right. One has already been completed for you.
(c(i))[1]
Name the positive ion with the lowest concentration.
(c(ii))[1]
State the name of the $\text{SO}_4^{2-}$ ion.
(c(iii))[1]
Calculate the mass of potassium ions in 125 cm$^3$ of polluted water.
(d)[4]
Name two substances used in treating the domestic water supply. For each one, state why it is used.
(e)[2]
Complete the symbol equation for the reaction between silicon(IV) chloride, SiCl$_4$, and water: SiCl$_4$ + $\ldots$H$_2$O $\rightarrow$ SiO$_2$ + $\ldots$HCl.