Question

25.) Three isotopes of an element have mass
numbers m, (m + 1) and (m + 2). If the mean
mass number is (m + 0.5) then which of the
following ratios may be accepted for m (m + 1)
(m + 2) in that order?​

Answer 1

Answer:

4:1:1

Let a,b, c be the relative abundances of three isotopes having mass numbers M, (M+1) and (M+2) respectively.

a+b+c

aM+b(M+1)+c(M+2)

=M+0.5

aM+bM+b+cM+2c=aM+bM+cM+0.5a+0.5b+0.5c

0.5b+1.5c=0.5a

b+3c=a

This is true for the option (B) a:b:c=4:1:1