Explanation:

- In the sentence, the idiom "Off and on" means doing something intermittently or at irregular intervals.

- Option 1: Rarely - This implies doing something not often or infrequently, but it doesn't capture the intermittent or repeated nature of "off and on".

- Option 2: Seldom - Similar to rarely, this means something that happens only occasionally and doesn't fully reflect the irregular intervals suggested by "off and on".

- Option 3: Immediately - This indicates doing something without any delay, which isn’t the intended meaning of "off and on".

- Option 4: Periodically - This means happening at intervals, which aligns well with the idiom's meaning.