Electrophilic substitution in phenols

All four compounds have a methyl group on the ring; they differ only in the second substituent, so reactivity depends on how strongly that group donates electrons to the ring.
$-OH$ donates its lone pair to the ring by a strong +R (resonance) effect and is a very powerful activating group.
$-OCH_3$ also shows a +R effect, but it is weaker than that of $-OH$ (+R effect: $-OH > -OCH_3$).
In $-NHCOCH_3$ the lone pair on nitrogen is also delocalised onto the carbonyl group, so its +R effect on the ring is reduced.
$-CH_2OH$ has no lone pair attached directly to the ring and cannot activate it by resonance.
Hence o-cresol (the compound with $-OH$) is the most reactive towards electrophilic reagents.

All four compounds have a methyl group on the ring and differ only in the second substituent, so the reactivity depends on how strongly that group releases electrons into the ring.
$-OH$ releases its lone pair into the ring by a strong +R effect; it is one of the most powerful activating groups.
$-OCH_3$ also has a +R effect, but slightly weaker than that of $-OH$.
In $-NHCOCH_3$ the nitrogen lone pair is shared with the adjacent C=O group, which reduces its donation to the ring.
$-CH_2OH$ has no lone pair directly attached to the ring, so it cannot activate the ring by resonance.
Hence o-cresol is the most reactive towards an electrophilic reagent.