A solution of H₂SO₄ acid is labelled is 95%. What is the mass of this that must be diluted with water to get 5L of solution containing 10g of H₂SO₄ per litre?

The solution is:

1L of the diluted solution must contain 10g of H2SO4.
Therefore, 5L of the diluted solution must contain 50g of H2SO4.
The concentration of the acid in the bottle is 95%.
This means that
95g of H2SO4 is present in 100g of the acid solution
50g of H2SO4 will be present in
50 * 100 / 95
52.64g of the solution