Question

Deuterium (21H) has a mass of 2.01355 u. What is the mass defect of deuterium?

a.) 0.00420 u
b.) 0.00024 u
c.) 0.00204 u
d.) 0.00402 u
e.) 0.00240 u

Answer 1

In dueterium when the proton and the neutron come together, their individual u amount is:
proton = 1.007276 u
neutron = 1.008665u
add the proton and neutron together for deuterium and the mass should be:
1.007276 u + 1.008665u = 2.015941u

but some mass was converted to energy so deuterium has mass 2.01355 u

So the mass defect is what the mass actually is from what it calculates to be before the fusion of neutron and proton:

2.015941 u - 2.01355 u = 0.002391 mass defect

so answer looks like..... e)