When 0.1 g of hydrogen is burnt in oxygen the number of water molecules produced is equal to?

We assume the reaction: 2 H₂ + O₂ → 2 H₂O. That means 2 molecules of H₂ produce 2 molecules of H₂O (stoichiometric 1:1).

Step-by-step: 

0.1 g of hydrogen (H₂) → number of moles = mass/molar mass = 0.1 g / (2.016 g/mol) ≈ 0.0496 mol. 

According to reaction each mole H₂ yields one mole H₂O (since 2 moles H₂ yield 2 moles H₂O). So you get ≈ 0.0496 mol of H₂O. 

Number of molecules = moles × Avogadro’s number (~6.022×10²³) → ≈ 0.0496 × 6.022×10²³ ≈ 2.99×10²² molecules. 

So about 3.0 × 10²² water molecules are produced (assuming complete reaction and excess oxygen).