36.Which mirror is used as rear view mirror in vehicles ?

37.Sparkling red colour after the blast of fire crackers is due to the presence of

38.The deficiency of Which one of the following gives rise to a disease characterised by oedema, subcutaneous haemorrhages, anaemia and pathological changes in the teeth and gums ?

39.The dufference between a nuclear reactor and an atomic bomb is that

40.Optical fibre works on the principle of