carbon dioxide

oxygen

hydrogen

nitrogen

0.1 ppm

0.01 ppm

0.001 ppm

0.0001 ppm

0.1 mg/litre

1.5 mg/litre

5 mg/litre

10 mg/litre

hardness in water

residual chlorine in water

turbidity in water

dissolved oxygen in water

only (i)

both (i) and (ii)

both (i) and (iii)

all (i), (ii) and (iii)