We know 1 mole of any atom or molecules contains [tex]6.033 \times 10^{23}[/tex] atom or molecules.
1 mole of HBr i.e 81 gm/mol contains [tex]6.033 \times 10^{23}[/tex] atom or molecules.
So, mass of [tex]9.03\times 10^{21}[/tex] molecules is :
[tex]m=\dfrac{81\times 9.03\times 10^{21} }{6.033 \times 10^{23}}\\\\m= 1.21\ gm[/tex]
Therefore, mass of [tex]9.03\times 10^{21}[/tex] molecules is 1.21 gm .
Hence, this is the required solution.
