In an urban atmosphere, the concentration of CH₄ and OH radical is 5 × 10¹⁹ molecules/m³ and 1.8 × 10¹² molecules/m³, respectively. The rate constant for the second-order reaction between OH and methane is 8.36 × 10⁻²¹ m³ molecule⁻¹ s⁻¹.
What is the instantaneous rate of oxidation of CH₄?

Correct option is C

The reaction between methane (CH₄) and hydroxyl radical (OH•) follows second-order kinetics, which can be expressed as:
Rate=k×[CH4​]×[OH•]
Where:
· k=8.36×10−21 m³ molecule⁻¹ s⁻¹ (rate constant)
· [CH4]=5.0×1019 molecules/m³
· [OH]=1.8×1012 molecules/m³
Now, substituting the values:

Additional Information:
· Second-order reactions depend on the concentration of both reactants, making their rate sensitive to changes in either.
· Methane (CH₄) oxidation by OH radicals is a key step in atmospheric chemistry, influencing the formation of greenhouse gases like CO₂.
· Hydroxyl radicals (OH•) are called "atmospheric detergents" as they help break down pollutants.