Physics
It is easier to carry two buckets of water in one hand each, than to carry only one in one hand because

Centre of gravity and centre of equilibrium fall within the feet
Centre of gravity falls within the body
Weights of buckets are balanced
Resultant weight of buckets is zero

ANSWER DOWNLOAD EXAMIANS APP

Physics
A hydrogen balloon floats up because of

Air pressure decreases with decrease in height
Air pressure decreases with decrease in weight
The pressure inside the balloon is more than the pressure outside it
Weight of the balloon is less than the weight of air displaced by it.

ANSWER DOWNLOAD EXAMIANS APP