22)
The molar mass of sucrose is measured to be 342.3 g. The value of Avogadro's number, correct to six significant digits, is 6.022 14 x 1023. The number of molecules in 0.24g of sucrose, written with an appropriate number of significant digits is
A) 4.2 x 1020
B) 4.22 x 1020
C) 4.222 x 1020
D) 4.222 4 x 1020

A) 4.2 x 10^20

Explanation:

All of the answers are pretty much the same so it comes down to significant digits.

You always go with the least number of significant digits that you have been given.

So 0.24g only has 2 so our answer will only have 2 significant digits.

If you want to know how to do the math here it is:

Avogadro's Number: 6.022 x 10^23

This number also equals 1 mole.

1 mole of sucrose is equal to 342.3g.

So the equation is set up like this:

0.24g x 1 mol / 342.3 g x 6.022 x 10^23 / 1 mol = 4.2 x 10^20 molecules.