Number-pairing trick: a Magistrate's Reception Order = 30 days, while admission under special circumstances by relatives = 90 days. The question specifies detention ordered by the Magistrate, so the figure to pick is 30 days. Knock out the distractors: 50 and 100 days are not statutory detention periods at all and are pure filler, so options 3 and 4 go. The 90-day option is the classic trap because it is a real period, but it applies to admission under special circumstances on a relative's application, not to a Magistrate's Reception Order, so option 2 is wrong here. The correct answer for the Magistrate's order is 30 days, option 1.