Ex4 10

$\def\abs#1{|#1|}\def\i{\mathbf {i}}\def\ket#1{|{#1}\rangle}\def\bra#1{\langle{#1}|}\def\braket#1#2{\langle{#1}|{#2}\rangle}\def\tr{\mathord{\mbox{tr}}}\mathbf{Exercise\ 4.10}$

Design a measurement on a $3$-qubit system that distinguishes between states in which the number of $1$ bits is even, and those in which the number of $1$ bits is odd, and gives no other information. Write all operators in bra/ket notation.