For jee exam most important thing is accuracy and time management . There is no need to solve each and every question by you should be sure about the answers you had selected that what matters .

Sir.,,No..it is not necessary to to attempt all the 30 questions in each subject....kind request is to attempt only confidential questions for the suitable answers..as there is negative mark u may lose mark...attempting a all the questions is good one.if and only if ur confidential..

I think this reason may clarify u r doubt sir..thank u