2.28 describe a physical test to show whether water is pure.

If water is pure it will boil at exactly 100° and freeze at exactly 0°

2.27 describe the use of anhydrous copper(II) sulfate in the chemical test for water

anhydrous copper sulphate will become hydrous copper sulphate when it is reacted with water.
So if anhydrous copper sulphate goes from white to blue in the presence of a liquid it will be water.

2.25 describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

acid + metal > salt + hydrogen

For example:
magnesium + hydrochloric acid > magnesium chloride + Hydrogen
Mg + 2HCl > MgCl2 + H2

2.26 describe the combustion of hydrogen

The combustion of hydrogen is its reaction with oxygen.
Water is created. and a lot of energy.
2H2 + O2 > 2H2O