the rightmost non-zero digit of the number 20^2520?

The zeros in this number will come only from 10 in the 20. Break the number in the following way-
(2X10)2520
All the zeroes will come from 10^2520
So the unit digit if 2^2520 is the rightmost non zero valu.
Now powers of 2 has cyclicity.
2,4,8,6,2,4,8,6...
You will notice that after every 4 terms, the series repeat. 2520 is divisble by 4. This means the last digit should be the forth term i.e 6.
So, 6 is the answer

2^2520mod10=2^4mod10=6