How many atoms are in 1.3g C? Answer in Units of Atoms

Okay, so first, let's turn the grams into moles.

1.3 g C / 12.011 g/mol = 0.1082341187 mol C

Next, we need to multiply it by Avogadro's Number for the number of atoms.

0.1082341187 mol C * 6.022*10^23 mol^-1 = 6.51785863*10^22 atoms C

Now we take significant figures into consideration. We started with two, so we need to end it with two.

6.5*10^22 atoms C

Explanation:

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.