In a homogeneous reaction A →B + C + D , the initial pressure
was P_{0} and after time t it was P.
expression for rate constant in terms of P_{0},
P and t will be

**A. **

**B. **

**C. **

**D. **

**Answer : ****Option A**

**Explaination / Solution: **

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If 75% of a first order reaction was completed in 60 minutes , 50% of the same reaction under the same conditions would be completed in

**A. ** 20 minutes

**B. ** 30 minutes

**C. ** 35 minutes

**D. ** 75 minutes

**Answer : ****Option B**

**Explaination / Solution: **

t_{75%} = 2t_{50%}

t_{50%} = (t_{75% }/
2) = (60/2) = 30 min

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The half life period of a radioactive element is 140 days. After 560 days , 1 g of element will be reduced to

**A. ** (1/2)g

**B. ** (1/4)g

**C. ** (1/8)g

**D. ** (1/16)g

**Answer : ****Option D**

**Explaination / Solution: **

In 140 days ⟹ initial concentration
reduced to (1/2)g

In 280 days ⟹ initial concentration
reduced to (1/4)g

In 420 days ⟹
initial concentration reduced to (1/8)g

In 560 days ⟹ initial concentration
reduced to (1/16)g

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The correct difference between first and second order reactions is that

**A. ** A first order reaction can be catalysed; a second order reaction cannot be catalysed.

**B. ** The half life of a first
order reaction does not depend on [A_{0}]; the half life of a second
order reaction does depend on [A_{0}].

**C. ** The rate of a first order reaction does not depend on reactant concentrations; the rate of a second order reaction does depend on reactant concentrations.

**D. ** The rate of a first order reaction does depend on reactant concentrations; the rate of a second order reaction does not depend on reactant concentrations.

**Answer : ****Option B**

**Explaination / Solution: **

For a first order
reaction

t_{1/2} =
0.6932/k

For a second order
reaction

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After 2 hours, a
radioactive substance becomes (1/16)^{th} of original amount. Then the
half life ( in min) is

**A. ** 60 minutes

**B. ** 120 minutes

**C. ** 30 minutes

**D. ** 15 minutes

**Answer : ****Option C**

**Explaination / Solution: **

4t_{1/2} = 2
hours

t_{1/2} = 30 min

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