Some moles of `O_(2)` diffuse through a small opening in 18 second. Same number of moles of an unknown gas diffuse through the same opening in 45 second. Molecular mass of the unknown gas is
A. `32 xx ((45)^(2))/((18)^(2))`
B. `32 xx ((18)^(2))/((45)^(2))`
C. `(32)^(2) xx (45)/(18)`
D. `(32)^(2) xx (18)/(45)`
