For the functioning of enzymes which of the following statements is not correct?

• An optimum temperature is needed

• An optimum pH is needed

• They are substrate specific

• They always increase activation energy

A chemical reaction is catalysed by 'X', therefore, 'X'

• increases the activation energy.

• does not affect the equilibrium constant of the reaction.

• decreases the enthalpy of the reaction.

• decreases the velocity constant of the reaction.

The half-life of a radioactive isotope is 3 h. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 h would be

• 8.0 gm

• 4.0 gm

• 12.0 gm

• 16.0 gm

The expression for velocity constant for the second order reaction is

• k = $\frac{2.303}{\mathrm{t}} {\log }_{10} \frac{\mathrm{a}}{\mathrm{a} -\mathrm{x}}$

• k = $\frac{1}{\mathrm{t}}\frac{\mathrm{x}}{\mathrm{a}(\mathrm{a} - \mathrm{x})}$

• k = $\frac{1}{\mathrm{t}}\frac{{\mathrm{x}}^2}{{\mathrm{a}}^2 [\mathrm{a} - \mathrm{x}{]}^2}$

• None of the above

The unit of rate constant for second order reaction is

• s^-1

• mol / L^-1

• L mol^-1 s^-1

• L² mol^-2 s

For a reaction of the type A + B → products, it is observed that doubling the concentration of A causes the reaction rate to be four times as great, but doubling the amount of B does not affect the rate. The rate equation is

• Rate = k[A][B]

• Rate = k[A]²

• Rate = k [A]²[B]

• Rate = k [A]²[B]²

Unit of first order rate constant is

• mol L s

• mol^-1 L^-1 s^-1

• mol L^-1 s^-1

• s^-1, min^-1 etc

Which of the following expression is correct for the first order reactions (C₀ refers to initial concentration and t_1/2 refers to half-life time)?

• ${\mathrm{t}}_{1/2} \infty {\mathrm{C}}_0^0$

• ${\mathrm{t}}_{1/2} \infty {\mathrm{C}}_0^{-1}$

• ${\mathrm{t}}_{1/2} \infty {\mathrm{C}}_0$

• ${\mathrm{t}}_{1/2} \infty {\mathrm{C}}_0^{1/2}$

459.

3A → 2B, rate of reaction $\frac{+\mathrm{d} \left(\mathrm{B}\right)}{\mathrm{dt}}$ is equal to

• $\frac{-3}{2}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $-\frac{2}{3}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $-\frac{1}{3}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $+2\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

2A → B + C

It would be a zero order reaction when

• the rate of reaction is proportional to square of concentration of A

• the rate of reaction remains same at any concentration of A

• the rate remains unchanged at any concentration of B and C

• the rate of reaction doubles if concentration of B is increased to double