Half and Average Life

Q. The half-life of ${}_6{C}^{14}$ if its K or \lambda is $2.31\times {10}^{-4}$ is

1. $2\times {10}^{2}yrs$
2. $3\times {10}^{3}yrs$
3. $3.5\times {10}^{4}yrs$
4. $4\times {10}^{3}yrs$

Q. Disintegration constant for a radioactive substance is $0.58h{r}^{-1}$. Its half-life period

1. 8.2 hr
2. 5.2 hr
3. 1.2 hr
4. 2.4 hr

Q.

A piece of wood was burned and 7.32 g of $C{O}_2$ was collected. The total radioactivity in $C{O}_2$ was 7.6 dpm. How old was the wood sample ? Given $t_{\frac{1}{2}}$ of C - 14 = 5730 years, specific activity of carbon obtained from a fresh wood sample is 15.2 dpm.

1. 5730 years

2. 11460 years

3. 22920 years

4. None of these

Q. The decay constant of ${}^{238}Uis1.54\times {10}^{-10}y{r}^{-1}$. What will be the average life of a sample of ${10}^{20}such{}^{238}U$ nuclei?

1. 3.25 billion years
2. 6.49 million years
3. 3.25 million years
4. 6.49 billion years

Q.

The radioactive decay, ${}_{83}B{i}^{211}\to {}_{81}T{l}^{207},$ takes place in 10 L closed container at $0^{\circ }C.$ Half - life of ${}_{83}B{i}^{211}$ is 2.15 min. Starting with 1 mole of ${}_{83}B{i}^{211}$, the pressure developed in the container after 4.30 min. will be

1. 16.8 atm

2. 22.4 atm

3. 2.24 atm

4. 1.68 atm

Q. In a sample of wood, the reading of a counter is $32\text{dpm}$ and in fresh sample of tree it is $122\text{dpm}$. Due to an error, the counter gives the reading 2 dpm in absence of ${}^{14}C$. The half-life of ${}^{14}C$ is 5770 years. The approximate age (in years) of wood sample is:

1. $7997.2$
2. $57,570$
3. $11,540$
4. $15140$

Q. The half-life period of radon is 3.8 days. After how many days will only one-twentieth of radon sample be left over?

1. 12.65 days
2. 24.75 days
3. 42.35 days
4. 6.5 days