Significant digits refer to the number of digits that are known versus the number of digits that are estimated. So if the number 20 is an approximation, there is only one significant digit, which is the 2. However, if 20 is accurate to the ones place, then there are 2 significant digits. 20.00 has four significant digits, because it is known that the number is accurate down to the hundredths place.
Avagadro's number is the amount of molecules in a mole. This is 6.022x10^23 molecules. There will be 6.022x10^20 molecules in a millimole and 6.022x10^14 in a nanomole. Therefore, the difference between these is how many molecules there are in the difference. This gives you approx 6.021994x10^20 molecules. This is limited by the amount of significant figures for avagadros number that I know of.
There are 5 significant figures in this number.
1 significant figure.
The answer depends on how many significant figures. To one sig fig it is 20.
It has two.
If your question was 'what is 216 to one significant figure', the answer would be 2. This is because the two means two hundred. If your number was 0.216 and you had to round it to one significant figure it would also be 2, but if your number is 0.203 and you had to round it to two significant figures you would say 20 this is because you only count the zeros as significant figures after an actual number. For example; 0.31 to two significant figures would be 31 but 0.301 to two significant figures would be 30.
It's 10, correct to two significant figures.
Integers ending in 0 are ambiguous. The answer is 1 or 2.
14.68 + 20
The number 20 million is expressed in figures as 20,000,000 - 2 followed by seven zeroes.