Solution:

(i) We use if and only if, in the bi conditional statement.

$p$: The unit digit of an integer is zero.

$q$: It is divisible by 5.

Therefore,

$p\leftrightarrow q =$ Unit digit of an integer is zero if and only if it’s divisible by 5.

Solution:

(ii) We use if and only if, in the bi conditional statement.

$p$: A natural number $n$ is odd.

$q$ : Natural number $n$ isn’t divisible by 2.

Therefore,

$p\leftrightarrow q =$ A natural number is odd if and only if it isn’t divisible by 2.