Which month of Hindi Year is called the “Brother of March”?

The correct option is Chate (Chaitra). Chaitra is the first month of the Hindi, or Vikram Samvat, calendar and customarily falls from March well into April. Since it ushically starts around the same time as the month of March in the Gregorian calendar, it is sometimes referred to as the “Brother of March.” The remaining months do not commonly match up with the month of March as well: Basakh falls in April–May, Magh in January–February, and Phaggan in February–March, so Chate is the correct option.