Question

The numbers of protons, electrons and neutrons in a molecule of heavy water are respectively:

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Answer 1

Heavy water is $D_{2}O$
Deuterium contains 1 proton, 1 neutron and 1 electron.
Oxygen contains 8 protons, 8 neutrons and 8 electrons.

Hence, for $D_{2}O$
Number of electrons =2+8=10
Number of protons =10
Molecular mass of $D_{2}O$ =4+16=20
hence,
$\text{Number of neutrons = Molecular mass - number of protons}$
$=20-10=10$

Hence, option (b) is correct.