Decomposition of H₂O₂ follows a first order reaction. In fifty minutes the concentration of H₂O₂ decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of H₂O₂ reaches 0.05 M, the rate of formation of O₂ will be:

• 6.93×10⁻⁴ mol min⁻¹

• 2.66 L min⁻¹ at STP

• 1.34×10⁻² mol min⁻¹

• 6.93×10⁻² mol min⁻¹

A.

6.93×10⁻⁴ mol min⁻¹

For first order reaction

Alternative Method:
If fifty minutes, the concentration of H₂O₂ decreases from 0.5 to 0.125 M or in one half-life, concentration of H₂O₂ decreases from 0.5 to 0.25 M. In two half-lives, concentration of H₂O₂ decreases from 0.5 to 0.125 M or 2t_1/2 = 50 min
t_1/2 = 25 min