Question

The total number of electrons present in $18mL$ of water is:

(Avogadro's number is $N_a$)

• A. $18N_a$
• B. $10N_a$
• C. $9N_a$
• D. $1N_a$

Answer 1

Answer: (B)

$10N_a$

The density of water is 18 g/mol.
18 mL of water corresponds to 18 g or 1 mole. They contain $N_a$ (Avogadro's number) of molecules.
Each water molecule contains total $2+8=10$ electrons (2 from $2$ $H$ atoms and $8$ from one $O$ atom).
Hence, $18$ mL of water will contain $10N_a$ electrons.