ï»¿ The mole

How many are A) $2$ moles of helium atoms ? B) $1.2 \cdot 10^{-13}$ moles of water molecules ?

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2 moles of helium atoms are $2 \cdot 6.023 \cdot 10^{23} = 1.205 \cdot 10^{24}$ helium atoms.

$1.2 \cdot 10^{-13}$ moles of water molecules are $1.2 \cdot 10^{-13} \cdot 6.023 \cdot 10^{23} = 7.408 \cdot 10^{10}$ water molecules.