The measurement 1020 ml contains four significant figures.
Here’s the breakdown: the digit ‘1’ is significant, as are both ‘0’s that follow it. The last ‘2’ is also significant. In general, leading zeros (zeros to the left of the first non-zero digit) are not counted as significant figures. However, in this case, there are no leading zeros.
When a measurement is expressed as a whole number followed by zeros (like 1020), all non-zero digits are significant, and any trailing zeros in a decimal context are also counted. Since there is no decimal point present, it’s still accepted that the trailing zeros indicate the precision of the measurement, thus counting them as significant.
To summarize, 1020 ml has four significant figures: 1, 0, 2, and the last 0.