What range of $pH$ is considered perfect for a fertile land?

Equal volumes of hydrochloric acid and sodium hydroxide solutions of the same concentration are mixed. The $pH$ of the resulting solution is checked with a $pH$ paper. What would be the colour obtained? (You may use the colour guide given in the figure.)

Write the chemical name and chemical formula of washing soda.

$A$ metal compound $'A'$ reacts with dilute sulphuric acid to produce a gas which extinguishes a burning candle. Identify the compound $'A'$ and the gas produced. Write a balanced chemical equation for the reaction if one of the compounds formed in the reaction is sodium sulphate.

As the concentration of $[H_{3}O^{+}]$ ions increases in an acidic aqueous solution,what happens to the nature of the solution?

Which of the following is not a mineral acid?