Question

 recently discovered and found to have an automatic weight of 342.38

Answer 1

Atomic weight of compound =342.38am

Mass of lighter isotope= 340.91amu

$\%$ abundance of lighter isotope

=68.322$\%$

Mass of lighter isotope in the compound

$= \frac{68.322}{100}x 340.91$

$= 232.9165amu$

Mass of heavier isotope in the compound

=342.38 - 232.9165

=109.4635amu

$\%$ abundance of heavier isotope

=$100\%-68.322\%$

=31.678$\%$

$\therefore\frac {31.678}{100}×$ mass of the heavier isotope

= 109.4635

$\implies$ mass of heavier isotope

$\frac {109.4635}{31.678}×100$

= 345.55 amu