<prompt> Infectivity of chicken pox last for :Till the last scab falls off6 days after onset of rash3 days after onset of rashTill the fever subsides  <response>: Period of communicability of varicella range from 1 to 2 days before the appearance of rash, and 4 to 5 days there after.Park 18e, p 123The patient ceases to be infectious once the lesions have crusted.Scabs are not infective. So, option a is wrong.Important features of chicken pox :Causative Agent - Varicella zoster virus HHV type 3Incubation period - 14 to 16 daysSecondary attack rate - 90Rash 