B. One
I believe that earth is the only planet that has life that we know of on it.
1. The Alpha particle is a helium nucleus, is positively charged & would barely penetrate a piece of paper.<span />
Answer:
n=6 to n=3 (B)
Explanation:
Energy of an electron present in the 
orbit is directly proportional to 
.Hence a transistion from one orbit to another orbit emits an energy proportional to the difference of their squares of the orbits. that is if an electron travels from orbit n1 to orbit n2 then it emits an energy corresponding to 
.So in the above question the highest energy emission occurs when an electron moves from n=6 to n=3.(Highest difference of energy levels).
