Question

The half-life period of a order reaction is 60 minutes What percentage will be left over after 240 minutes ?

• A. $6.25\%$
• B. $4.25\%$
• C. $5\%$
• D. $6\%$

Answer 1

Answer: (A)

Given, $t_{1/2}=60$ min

Number of half-lives (n),

$T=n\times t_{1/2}$

$\therefore n=\frac{T}{t_{1/2}}=\frac{240}{60}=4$

Let the initial amount be 100

Then amount left (a-x) after four $(n=4)$

half-lives $=\frac{100}{2^n}$

$(a-x)=\frac{100}{c^4}=\frac{100}{16}$

$(a-x)=6.25\%$