Suppose 20 atoms of hydrogen react with chlorine to produce 20 molecules of hydrochloric acid according to the law of conservation of matter how many atoms of chlorine reacted with the hydrogen would it be 20 or 40 or 10 or zero

To determine how many atoms of chlorine reacted with the 20 atoms of hydrogen to produce 20 molecules of hydrochloric acid (HCl), we can look at the balanced chemical equation for the reaction:

\[ \text{H}_2 + \text{Cl}_2 \rightarrow 2 \text{HCl} \]

From this equation, we can see that 1 molecule of hydrogen gas (H₂) reacts with 1 molecule of chlorine gas (Cl₂) to produce 2 molecules of hydrochloric acid (HCl).

If we are starting with 20 atoms of hydrogen (which is equivalent to 10 molecules of H₂ since each molecule consists of 2 hydrogen atoms), we can determine the amount of chlorine that would react:

- For every 1 molecule of H₂ (which contains 2 hydrogen atoms), 1 molecule of Cl₂ is required.
- 1 molecule of Cl₂ contains 2 chlorine atoms.

Since 10 molecules of H₂ are present (from 20 hydrogen atoms), it would take 10 molecules of Cl₂ to react completely with them. This means:

- 10 molecules of Cl₂ contain \( 10 \times 2 = 20 \) chlorine atoms.

Therefore, the number of chlorine atoms that reacted is **20 atoms of chlorine**.