Here is the order of increasing reactivity toward nitration is
a) acetophenone
c) bromobenzene
c) acetanilide
d) toluene

Nitration is electrophilic substiuion reaction and reactivity of benzene ring towards nitration depends on the type of substituent atteached. This reaction is typical of the aromatic ring, and derivatives of benzene, C6H5G, behave similarly. The reaction depends on the group attached whether it is electron donating or electron withdrawing and is the group G an activating group or a deactivating group.
Here, acetophenone and bromobenzene are enectron withdrawing,
while acetanilide and toluene are electron donating with toluene being 25 times more reactive than its parent compound i.e benzene.