Assertion (A): tropylium bromide, $C X_{7} H X_{7} X^{+} Br X^{-}$ , is an ionic, water-soluble salt, unlike an ordinary alkyl bromide. Reason (R): the cycloheptatrienyl cation is planar and cyclic with 6 delocalised pi electrons, so it is aromatic and unusually stable.

Answer: C

Loss of bromide from cyclohepta-1,3,5-triene-7-yl bromide gives a planar cation with 6 pi electrons over 7 carbons (

4 n + 2

n = 1

). This aromatic stabilisation makes the cation so stable that the compound exists as an ionic salt, so both statements are true and R explains A.