How is an aqueous solution with $pH = 2$ compared to an aqueous solution with $pH = 4$?

The $.........$ of the molar concentration of $[H_3O^+]$ in an acidic aqueous solution is called the $pH$ of that solution.

$(a)$ Study the following chemical equation:
$CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
Name the reactant and the product. State one use of the product.

$(a)$ What will you observe when dilute hydrochloric acid is added to a small amount of copper oxide in a beaker?
$(b)$ Aqueous solution of $HCl$ shows acidic character. But the aqueous solution of glucose fails to do so. Why?

How would you distinguish between baking powder and washing soda by heating?

The $pH$ scale is applicable to which of the following?