Why does the core of the sun contain more helium and less hydrogen than the surface of the sun?

What are the factors that affect the resistance of a wire?

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?

Examine the nuclear reacti why is this classified as a nuclear reaction rather than a chemical reaction? it is not balanced. a new compound is formed. a change has occurred in a nucleus. a new element has been formed.