Question

The average atomic weight of an element is 39.1 a.m.u. It contains isotopes of 39, 40 and 41 a.m.u. The abundance of isotope with 40 a.m.u is 0.012%. The relative abundance of other two isotopes will be –

• A. 94.994, 4. 994
• B. 93.700, 6.233
• C. 93.173, 6.915
• D. None of these

Answer 1

Answer: (A)

94.994, 4. 994

Answer 2

Suppose abundance of isotope of 39 a.m.u is x%.

\ = 39.1

Ž = 39.1

Ž – 2x + 4100 – 0.012 = 3910

Ž 190 – 0.012 = 2x = 189.988

\ x = $\frac { 189.988 } { 2 }$= 94.994%