Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?

Given, ratio of H : O by mass to form water = 1 : 8
\(\Rightarrow \) 1 g of hydrogen required 8 g of oxygen to react completely.

We have to find the mass of oxygen that is required to completely react with 3 g of hydrogen.

So, 3 g of hydrogen will require \( (8 × 3) \)g of oxygen

\(\therefore \) 24 g of oxygen is required to completely react with 3 g of hydrogen.