1. The number of electrons in 18 ml of H2O is
a. 60.23 x 1023
b. 6.023 x 1023
c. 3.011 x 1023
d. 0.6023 x 1023
Number of Electrons in 18 mL of H2O: CSIR NET Solved MCQ
18 mL of water contains exactly 1 mole of H₂O molecules, leading to 10 × 6.023 × 10²³ electrons total. The correct option is a. 60.23 × 10²³, equivalent to 6.023 × 10²⁴ electrons.
Step-by-Step Solution
Density of water is 1 g/mL, so mass = 18 mL × 1 g/mL = 18 g. Molar mass of H₂O is 18 g/mol, giving 18/18 = 1 mole. One mole contains Avogadro’s number of molecules: 6.023 × 10²³ H₂O molecules. Each H₂O has 10 electrons (2H × 1 + O × 8), so total electrons = 6.023 × 10²³ × 10 = 6.023 × 10²⁴ = 60.23 × 10²³.
Option Analysis
-
a. 60.23 × 10²³: Correct, matches 10 × N_A (Avogadro’s number).
-
b. 6.023 × 10²³: Counts only molecules, ignores 10 electrons per molecule.
-
c. 3.011 × 10²³: Half of molecules (error in mole or atom count).
-
d. 0.6023 × 10²³: One-tenth molecules (forgets multiplication by 10).
