The partial pressure of \[C{{O}_{2}}\] in air saturated with water vapours at \[25{}^\circ C\] and 1.00 atm is \[3.04\times {{10}^{-4}}\] atm. Henry's constant for \[C{{O}_{2}}\] in water is \[2.3\times {{10}^{-2}}\,\text{mol}\,{{\text{L}}^{-1}}\text{at}{{\text{m}}^{-1}}\] and for carbonic acid \[p{{K}_{a}}\] is 6.37. The pH of normal (\[C{{O}_{2}}\] mixed) rain water will be

• A. 7.42
• B. 6.37
• C. 6.99
• D. 5.76