What is the radius of iodine atom? (atomic no. 53, mass no. 126) [1988]

1. $2.5\times {10}^{-11} m$

2. $2.5\times {10}^{-9} m$

3. $7\times {10}^{-9} m$

4. $7\times {10}^{-6} m$

Which of the following statements is true for nuclear forces? [1990]

1. They obey the inverse square law of distance.

2. They obey the inverse third power law of distance.

3. They are short range forces.

4. They are equal in strength to electromagnetic forces.

Bragg's law for X-rays is:

1. dsin$\theta$ = 2n$\lambda$ 

2. 2dsin$\theta$ = n$\lambda$

3. nsin$\theta$ = 2$\lambda$d

4. None of these

The relationship between disintegration constant $\left[\lambda \right]$ and half-life [T] will be:

1. $\lambda =\frac{{\log }_{10} 2}{T}$ 

2. $\lambda =\frac{{\log }_e 2}{T}$

3. $\lambda =\frac{T}{{\log }_e 2}$   

4. $\lambda =\frac{{\log }_2 e}{T}$

Alpha particles are 

1. 2 free protons

2. helium atoms

3. singly ionized helium atoms

4. doubly ionised helium atoms

A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier? 

1. 1.0 microcurie       

2. 0.5 microcurie           

3. 4 microcurie             

4. 8 microcurie

A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain? 

1. $\frac{1}{2}$

2. $\frac{1}{16}$ 

3. $\frac{1}{8}$ 

4.$\frac{1}{256}$

In a given reaction,

${}_{Z}X_A\to {}_{Z+1}Y_A\to {}_{Z-1}K_{A-4}\to {}_{Z-1}K_{A-4}$

Radioactive radiations are emitted in the sequence of  

1.  $\alpha , \beta , \gamma$ 

2. $\gamma , \alpha , \beta$ 

3. $\beta , \alpha , \gamma$ 

4. $\gamma , \beta , \alpha$

An observer A sees an asteroid with a radioactive element moving by at a speed = 0.3 c and measures the radioactivity decay time to be $T_A$. Another observer B is moving with the asteroid and measures its decay time as $T_B$. Then $T_A$ and $T_B$ are related as below [VITEEE 2008]

1. $T_B$ < $T_A$

2. $T_B$ = $T_A$

3. $T_B$ > $T_A$

4. Either 1 or 3 depending on whether the asteroid is approaching or moving away from A.