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

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

188.

A hydrogenation reaction is carried out at 500 K. If the same reaction is carried out in the presence of a catalyst at the same rate, the temperature required is 400 K. If the catalyst lowers the activation barrier by 40 kJ mol^-1 the activation energy of the reaction will be

• 100 kJ mol^-1

• 200  kJ mol^-1

• 300 kJ mol^-1

• 175 kJ mol^-1

A radioactive sample is emitting 64 times radiations than non-hazardous limit. If its half life is 2h, after what time it become non-hazardous?

• 16h

• 12h

• 8h

• 4h

Order of reaction is decided by

• molecularity

• pressure

• temperature

• mechanism of reaction as well as relative concentration of reactants