Emergency contraceptives are effective if administered within following period after unprotected intercourse:

Ans. is d, i.e. 120 hoursRef: Shaw 15th/ed, p237; Current Concepts in Contraception and Women Death, pl05, Leon Speroff8th/ed, p1042The standard recommendation is to start emergency contraceptive not later than 72 hours. The greatest protection is offered, if it is taken within 12 hours, as postponing the dose by 12 hours raises the chances of pregnancy by almost 50%.For this reason, the treatment should be initiated as soon as possible after sexual exposure.Note: But here the question says - till how long are ECs effective or till how long can they be administered. - Ref: Shaw 14th/ed, p213 says"The tables can be offered up to 120 hours, but its efficacy decreases with the longer coital - drug interval.""Treatment should be initiated as soon after exposure as possible, and the standard recommendation is that it be no later than 120 h." - Ref: Leon Speroff 8th/ed, p1042 According to current concepts in contraception's and women health alsoEmergency contraception can be given up to 5 days.This is because"Emergency contraception is not an abortifacient i.e. it will not act after implantation has occured. This is also the basis for the window period of 5 days for use effectiveness of EC, as the whole process from deposition of sperms to implantation takes about 5 days." - Ref: Current Concepts in Contraception and Women Health p108