Observation

Many candidates attempted this question and their performance was good. In part (a) (i) many candidates could correctly explain purification of water. In part (a) (ii) many candidates correctly mentioned sources of portable water supply. In part (b) many candidates were able to mention substances that can cause atmospheric pollution.
The expected answers are as follow:
7.         (a)        (i)        Purification of water

-           is a process of removing dirty / harmful / contaminated substances from water to make it drinkable / potable / suitable / safe for drinking
-           is the removal of foreign materials / bacterial / microorganisms from water
to make it drinkable / potable / suitable / safe for drinking

(ii)             Sources of potable water

-           tap water / pipe borne water
-           borehole / well water
-           spring water

(b)       Substances that can cause atmospheric pollution

-           burning of coal/wood/refuse/bush
-           burning/flaring of oil and gas
-           dust
-           chemical pollutant /  herbicide / aerosol / insecticide
-           noise by vehicles, aircrafts, heavy machines
-           radiation
-           home furnace
-           smoke from vehicles / soot / grit / carbon monoxide
-           odour from refuse dumps