Correct Answer - C
We know that the distance between parallel planes `ax+by=cz+d_(1)=0` and `ax+by+cz+d_(2)=0` is given by
`(|d_(1)-d_(2)|)/(sqrt(a^(2)+b^(2)+c^(2)))`
Here the planes are `2x+y+2z-8=0` and `2x+y+2z+5/2=0`
`:.` Required distance `=|(|-8-5/2|)/(sqrt(2^(2)+1^(2)+2^^(2)))|=7/2`