The half-life period (t_1/2) for ²⁴¹Am in years, (given that it emits 1.2 × 10¹¹ α-particles per gram per second) is

• 375 yr

• 112 yr

• 615 yr

• 458 yr

If the initial concentration of the reactant is doubled, the time for half reaction is also doubled. The order of the reaction is

• zero

• one

• two

• three

The rate of a reaction doubles when the initial concentration of the reactant is made four fold. If the initial concentration is made 400 fold, then the rate will become

• 400 times

• 200 times

• 40 times

• 20 times

A radioactive element has half-life 150 yr. A sealed tube containing 1.0 g of sample will contain after 300 yr will be

• 1.0 gm

• 0.5 gm

• 0.25 gm

• 0.125 gm

For the reaction,

2NO + Br₂ $\to$ 2NOBr

the following mechanism has been given

NO + Br $\stackrel{\mathrm{fast}}{\to }$ NOBr₂

NOBr₂ + NO $\stackrel{\mathrm{slow}}{\to }$ 2NOBr

Hence, rate law is

• k[NO]²[Br₂]

• k[NO][Br₂]

• k[NOBr₂][NO]

• k[NO][Br₂]²

The rate constant of a reaction is given by $\frac{{\mathrm{N}}_{\mathrm{t}}}{{\mathrm{N}}_{\circ }}= {\mathrm{e}}^{-\mathrm{Kt}}$ . This represents for reaction of

• zero order

• second order

• first order

• None of these

The half-life of a radioactive element depends upon

• amount of element

• temperature

• pressure

• independent

488.

75% of a first order reaction was completed in 32 min. When was 50% of the reaction completed?

• In 16 min

• In 24 min

• In 8 min

• In 4 min

The activation energy of a reaction is zero. The rate constant of this reaction

• Increases with an increase of temperature

• decreases with an increase of temperature

• decreases with decrease of temperature

• is independent of temperature

The velocity of a moving electron having 4.55 × 10^-25 J of kinetic energy is

• 10³ m s^-1

• 10⁵ cm s^-1

• 10² m s^-1

• 10⁴ cm s^-1