Question -
What is the number of oxygen atoms present in 126 g of HNO3?
Options:
A .  36.132×1023
B .  9.033×1023
C .  120.44×1023
D .  16.132×1023
Answer: Option A : A Molecularmass of HNO3 = atomic mass of hydrogen + atomic mass of nitrogen + 3× atomic mass of oxygen = 1 + 14 + (3 × 16) = 63 u. Number of moles = GivenmassGrammolecularmass Moles of HNO3= 12663 = 2 moles ∙ In 1 molecule of HNO3we have 3 atoms of oxygen. ∙ 1 mole of HNO3 contains 3 moles of oxygen atoms. So, in2 moles ofHNO3 we will have 6 moles of oxygen atoms. ∙ One mole of a substance contains6.022×1023 particles. So, the number of atoms in 126 g of HNO3= 6×6.022×1023 = 36.132×1023 atoms.
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