He makes occasional visits to Delhi.

Answer: Option C

Occasional : occurring, appearing, or done infrequently and irregularly.
Accidental : happening by chance, unintentionally, or unexpectedly.
Strange : unusual or surprising; difficult to understand or explain.
Regular : arranged in or constituting a constant or definite pattern, especially with the same space between individual instances.
Frivolous : not having any serious purpose or value.

Antonym of Occasional is Regular