What is the mass of 14.1 mol of the element nickel (Ni)

Also, How many molecules are contained in 0.900
mol O2?

How many molecules are in 7.00 mol He?

What is the mass of 0.0401 mol of the element
sodium (Na)?

How many molecules are in 0.0690 mol NH3?

and
How many molecules are in 23.2 g NO2?

I just did over 30 problems so my brain is fried and I just have these left. thanks/

How many molecules are in 23.2 g NO2?

23.2 g / 46.005 g/mol = 0.504293 mol

0.504293 mol times 6.022 x 10^23 molecules/mol = 3.14 x 10^23 molecules (to three sig figs)

You have some other problems that ask about how many molecules in some amount of moles. Just do the second step in the above solution for those other problems.
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What is the mass of 0.0401 mol of the element sodium (Na)?

0.0401 mol times 22.99 g/mol = 0.922 g

Fried brain? Take an ice cream break. Best wishes on the test!