Question

How many grams are in 0.040 moles zirconium (Zr)? Only 2 significant numbers?

Answer 1

Mass of Zirconium (Zr) in 0.040 moles : 3.6 g

Further explanation  

The mole is the number of particles(molecules, atoms, ions) contained in a substance  

1 mol = 6.02.10²³ particles

Can be formulated

N=n x No

N = number of particles

n = mol

No = Avogadro's = 6.02.10²³

Moles can also be determined from the amount of substance mass and its molar mass

$\tt n(mol)=\dfrac{m(mass)}{MW(molecular~weight)}$

moles of Zirconium : 0.04

mass of Zirconium (MW=91,224 g/mol) :

$\tt mass=mol\times MW\\\\mass=0.04\times 91,224\\\\mass=3.6~g$