How many moles of argon, Ar, are in 1.31×1024 Ar atoms?

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

i'm pretty sure it is letter c.) car

1.43 x 10^-11 j the guy commented the awnser just making sure u see it .