A vessel contains `14` g (`7` moles ) of hydrogen and `96` g (`3`moles) of oxygen at `STP`. Chemical reaction is induced by passing electric spark in the vessel till one of the gases is consumed. The temperature is brought back to it's starting value `273 K` .The pressure in the vessel is-

Options

A. 0.1 atm
B. 0.2 atm
C. 0.3 atm
D. 0.4 atm

Answer

A

Explanation

If electric spark is passed, hydrogen reacts with oxygen to form water `(H_2O)`.
Each gram of hydrogen reacts with eight grams of oxygen.
The gas left in the vessel will be 2 gm of hydrogen i.e. no. of moles ` = 2/2 = 1`
(`:. 96/9 = 12 gm` consumed hydrogen)
Initial no. of moles = 7 + 3 = 10 moles.
`:. p_2/p_1 = n_2/n_1 rArr P_2 = 1/10 = 0.1 atm`.