What is the mass (g) of 0.25mols of NaCl?

What you need for these equations are a calculator, periodic table and the following equation:

Mass (g) = Mr x Moles     (important equation to remember)

In this case we already know the moles as it's in the question, 0.25 moles. 

to find the Mr, you need to look at your periodic table. Find the relative atomic mass of Na and Cl and add the two numbers together. 

Na = 22.99

Cl = 35.45

NaCl = 58.4

Now just put all of the numbers into the equation. 

0.25 x 58.4 = 14.6g