4 moles each of `SO_(2)` and `O_(2)` gases are allowed to react to form `SO_(3)` in a closed vessel. At equilibrium, 25% of `O_(2)` is used up. The total number of moles of all the gases at equilibrium is

Options

A. `6.5`
B. `7.0`
C. `8.0`
D. `2.0`

Answer

B

Explanation

Moles of `O_(2)` used up = 25 % of 4 = 1 mol.
`{:(,2SO_(2),+,O_(2),hArr,2SO_(3)),("Initial moles",4,,4,,0),("Moles at eqm.",4-2,,4-1,,),(,=2,,=3,,2):}`
Therefore total number of moels of all gases at
eqm. = 2+3+2 = 7