Answer:
One significant number.
Step-by-step explanation:
If a number doesn't contain decimal then we should always follow the rules to find the significant digits.
1). Leading zeros doesn't count.
2). All non zero numbers and zeros between the non zero numbers will be counted as significant digits.
3). Trailing zeros will not be counted if there is no decimal after the zeros.
In this question,
20 has one significant number because after 2 (non zero number) 0 will not be counted as significant number [By rule number (3)]
