JEE Main · 2021 · 26 Feb 2021 · Shift 1 · Some Basic Concepts of Chemistry

A power of ten only moves the decimal point and carries no significant figures of its own, so the count is made on the digits of $50000.020$.
A number written with a decimal point and with digits after it keeps all of its digits as significant: the leading $5$, the four zeros that complete the whole number part, the zero in the first decimal place, the $2$, and the trailing zero after it.
Counting $5,0,0,0,0,0,2,0$ gives $8$ significant figures.