$A$ sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?

What are strong and weak acids? In the following list of acids,separate strong acids from weak acids: Hydrochloric acid,citric acid,acetic acid,nitric acid,formic acid,sulphuric acid.

Write balanced chemical equations for the following:
$(i)$ Bleaching powder is kept open in air.
$(ii)$ Blue crystals of copper sulphate are heated.
$(iii)$ Chlorine gas is passed through dry slaked lime.

What are olfactory indicators?

Identify $A, B$ and $C$ in the following reactions and write the chemical name of $A, B$ and $C$.
$(i)$ $HNO_{3} + NaOH \rightarrow \underline{A} + H_{2}O$
$(ii)$ $\underline{B} + Ca(OH)_{2} \rightarrow CaSO_{4} + 2H_{2}O$
$(iii)$ $HCl + \underline{C} \rightarrow KCl + H_{2}O$

Which of the following is not a mineral acid?