10) B

We must first write down the full equation for the reaction.

2Na + 2H2O -> 2NaOH + H2

Moles of Na = m/Mr = (1.15÷23) ≈ (1.2÷24) = 0.05 mol
Molar ratio (NaOH:H2) = 2:1
Moles of H₂ = (0.05÷2) = 0.025mol

We know 1 mol gives 22.4dm3 of gas
0.025 mol = 22.4 x 0.025 = 0.56 dm3
1dm3 = 1000cm3
0.56 dm3 = 560cm3

The answer is B