${}_{11}\mathrm{Na}^{24}$ is radioactive and it decays to 

• ${}_9\mathrm{F}^{20} \mathrm{and} \mathrm{\alpha }- \mathrm{practicle}$

• ${}_{13}\mathrm{Al}^{24} \mathrm{and} \mathrm{positron}$

• ${}_{11}\mathrm{Na}^{23} \mathrm{and} \mathrm{neutron}$

• ${}_{12}\mathrm{Mg}^{24} \mathrm{and} \mathrm{\beta }- \mathrm{parcticles}$

The paramagnetic behaviour of B₂ is due to the presence of

• two unpaired electrons in ${\mathrm{\pi }}_{\mathrm{b}}$ MO

• two unpaired electrons in $\stackrel{*}{\mathrm{\pi }}$ MO

• two unpaired electrons in $\stackrel{*}{\mathrm{\sigma }}$ MO

• two unpaired electrons in ${\mathrm{\sigma }}_{\mathrm{b}}$ MO

A 100 mL 0.1 = (M) solution of ammonium acetate is diluted by adding 100 mL of water. The pH of the resulting solution will be (pK_a of acetic acid is nearly equal to pK_b of NH₄OH).

• 4.9

• 5.0

• 7.0

• 10.0

Which one of the following characteristics belongs to an electrophile?

• It is any species having electron deficiency which reacts at an electron rich C-centre

• It is any species having electron enrichment, that reacts at an electron deficient C-centre

• It is cationic in nature

• It is anionic in nature

Equal weights of CH₄ and H₂ are mixed in an empty container at 25°C. the fraction of the total pressure exerted by H₂ is

• 1/9

• 1/2

• 8/9

• 16/17

In a reversible chemical reaction at equilibrium, if the concentration of any one of the reactants is doubled, then the equilibrium constant will

• also be doubled

• be halved

• remains the same

• becomes one-fourth

Identify the correct statement from the following in a chemical reaction

• The entropy always increases

• The change in entropy along with suitable change in enthalpy decides the rate of reaction

• The enthalpy always decreases

• Both the enthalpy and the entropy remain constant

Which one of the following is wrong about molecularity of a reaction?

• It may be whole number or fractional

• It is calculated from reaction mechanism

• It is the number of molecules of the reactants taking part in a single step chemical reaction

• It is always equal to the order of elementary reaction

Which of the following does not represent the mathematical expression for the Heisenberg uncertainty principle?

• $∆\mathrm{x}·∆\mathrm{P}\ge \mathrm{h}/ \left(4\mathrm{\pi }\right)$

• $∆\mathrm{x}·∆\mathrm{\nu }\ge \mathrm{h}/\left(4\mathrm{\pi m}\right)$

• $∆\mathrm{E}·∆\mathrm{t}\ge \mathrm{h}/\left(4\mathrm{\pi }\right)$

• $∆\mathrm{E}·∆\mathrm{x}\ge \mathrm{h}\left(4\mathrm{\pi }\right)$

The stable bivalency of Pb and trivalency of Bi is

• due to d contraction in Pb and Bi

• due to relativistic contraction of the 6s orbitals of Pb and Bi, leading to inert pair effect

• due to screening effec

• due to attainment of noble liquid configuration