A negatively charged balloon has 4.3 µc charge. How many excess electrons are on this balloon? The elemental charge is 1.6 x 10-19 C.

Q = N * e       excess charge due to N electrons

N = Q / e = 4.3E-6 C / 1.6E-19  C = 2.69^13 electrons

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.