Answer:
2.1 x 10^24
Explanation:
The number of atoms in a mole will always be the same. The fact that it's lithium is completely irrelevant.
One mole of anything is 6.022 x 10^23 atoms
So if we need to find the number of atoms in 3.5 mol we just need to multiply Avogadro's number by 3.5
3.5 x 6.022 x 10^23
= 21.077 x 10^23
To make it proper scientific notation the first number can't be greater than 10 so let's move the decimal place and increase the exponent
2.1077 x 10^24
Remove the numbers that aren't significant figures
2.1 x 10^24
Boom there's your answer
