1g of Mg is burnt in a vessel containing 0.5g of oxygen. The reactant remaining unreacted is

When 1g Mg reacts with oxygen, we analyze the stoichiometry of the reaction between magnesium (Mg) and oxygen (O₂), forming magnesium oxide (MgO). The balanced chemical equation is:

2Mg + O₂ → 2MgO

From the equation, we see that 24g of Mg reacts with 16g of O₂ completely. Now, we calculate the amount of Mg that reacts with 0.5g of O₂:

16g O₂ reacts with 24g Mg.

0.5g O₂ reacts with = \( \frac{24 \times 0.5}{16} = 0.75 \)g of Mg.

This means only 0.75g of the 1g Mg is consumed in the reaction. The unreacted Mg is calculated as:

Unreacted Mg = 1g Mg - 0.75g Mg = 0.25g Mg.

Conclusion:

After the reaction, 0.25g of the 1g Mg remains unreacted. This is because there is insufficient oxygen (0.5g O₂) to completely react with 1g Mg.