How will you distinguish:
Benzaldehyde and acetophenone

Explanation

Pentan-2-one `(CH_(3)COCH_(2)CH_(2)CH_(3))` and Pentain-3-one `(CH_(3)CH_(2)COCH_(2)CH_(3))`.
Pentan-2-one contains `CH_(3)CO` group and as such it will give iodoform test NaOI `[NaOH + I_(2)]` while no such group is there in pentan-3-one and as such it will not give iodoform test.
`underset("Pentan-2-one")(CH_(3)COCH_(2)CH_(2)CH_(3)) + underset(("form NaOH " + I_(2)))(3NaOI) rarr CH_(3)CH_(2)CH_(2)COONa + underset("Iodoform (yellow ppt.)")(CHI_(3)) + 2NaOH`
`underset("Pentan-3-one")(CH_(3)CH_(2)COCH_(2)CH_(3)) + NaOI rarr No` yello ppt.