Question

How many electrons are present in $2\times {10}^{-3}$ moles of ${}_8^{18}{O}^{2-}$ ?

• A. $1.2\times {10}^{21}$
• B. $9.6\times {10}^{21}$
• C. $1.2\times {10}^{22}$
• D. $1.9\times {10}^{22}$

Answer 1

Answer: (C)

$1.2\times {10}^{22}$

${}_8^{18}{O}^{-2}\Rightarrow$ total no of electrons =8+2

=10

1 mole of${}_8^{18}{O}^{-2}$ has $10\times 6.023\times {10}^{23}$ electrons

$2\times {10}^{-3}$ moles of ${}_8^{18}{O}^{-2}$ has $x$electrons

$x=10\times 6.023\times {10}^{-23}$

$x=1.2\times {10}^{22}$