An element, X has the following isotopic composition; 200 X: 90 % 199 X: 8.0 % 202 X: 2.0 % The weighted average atomic mass of the naturally-occurring element X is closest to:

Question

An element, X has the following isotopic composition; 200 X: 90 % 199 X: 8.0 % 202 X: 2.0 % The weighted average atomic mass of the naturally-occurring element X is closest to: (A) 201 amu (B) 202 amu (C) 199 amu (D) 200 amu

Tardigrade Admin · Accepted Answer

Weight of 200X = 0.90 × 200 = 180.00 u Weight of 199X = 0.08 × 199 = 15.92 u Weight of 202X = 0.02 × 202 = 4.04 u Total weight = 199.96 ≈ 200 u

Q. An element, $X$ has the following isotopic composition;
$^{200} X : 90%$
$^{199} X : 8.0%$
$^{202} X : 2.0%$
The weighted average atomic mass of the naturally-occurring element $X$ is closest to:

201 amu

202 amu

199 amu

200 amu

Weight of $^{200} X = 0.90 \times 200 = 180.00 u$
Weight of $^{199} X = 0.08 \times 199 = 15.92 u$
Weight of $^{202} X = 0.02 \times 202 = 4.04 u$
Total weight $= 199.96 \approx 200 u$

Q. An element, X has the following isotopic composition; 200X:90% 199X:8.0% 202X:2.0% The weighted average atomic mass of the naturally-occurring element X is closest to: