Answer:
[tex] \underline{ \boxed{12.5 g }}\: of \: (thorium-234 ) \\ \: would \: remain \: from \: \\ 100 g \: after \: 72 \: days[/tex]
Explanation:
[tex]if \: (Thorium-234) \: has \: a \: (half-life )\: of \: 24 \: days \\ then \: : it \: will \: disintegrate \: into \: \frac{1}{2} \: of \: 100g \\ but \: after \: 72 \: days \: i.e \: (24 \times 3)days \\ it \: will \: reduce \: to\:half \: its \: original \: ( \times 3) \\ hence \to \: \\ \frac{100}{ {2}^{3} } = \frac{100}{8} = \frac{25}{2} = \underline{ \boxed{12.5g}}[/tex]
