Question

Natural water contains about $0.02\%$ $D_{2}O$ (heavy water). When it is enriched to $20\%$ (by volume), calculate the fraction of weight due to neutrons in 1 mole of sample.

• A. $0.355$
• B. $0.444$
• C. $0.455$
• D. $0.500$

Answer 1

The correct option is C $0.455$

Assume total sample is of $100gm$

Now, $20gm=D_{2}O$ and $80gm=H_{2}O$,

Mass of neutrons in $80gm$ of $H_{2}O=\frac{320}{9}$

mass of neutrons in $20gm$ of $D_{2}O=\frac{100}{11}$

Fraction of weight $=\frac{\frac{320}{11}+\frac{100}{11}}{100}=.455$