Consider the following statements:

a. Both acids and bases change colour of all indicators.

b. If an indicator gives a colour change with an acid, it does not give a change with a base.

c. If an indicator changes colour with a base, it does not change colour with an acid.

d. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

i. All four ii. a and b

iii. b and c iv. Only d

All indicators do not change colour with acids as well as bases, e.g. turmeric changes its colour to pink with base but it remains yellow with acid. Litmus paper, methyl orange are some indicators which changes colour with both acids and bases.