Correct Answer - A
From FBD of block, `N=mg cos theta`
`p+f=mg sing theta or f=mg sin theta-P`
As P varies from `mg(sin theta-mu cost thea) "to" mg (sin theta+mu cos theta)`
`"f varies from"+mu m g cos theta "to"- mu mg cos theta`
This value of friction is always less than equal to `muN` is magnitude. Hence, option (a) is correct