Lead is the final product formed by a series of changes in which the rate determining stage is the radioactive decay of- uranium-238 with a half-life of 4.5 × 10⁹ yr. What would be the age of a rock sample originally lead free in which the molar proportion of uranium to lead is now 1 : 3?

• 1.5 × 10⁹ yr

• 2.25 × 10⁹ yr

• 4.5 × 10⁸ yr

• 9.0 × 10⁹ yr

An 1% solution of KCl (I), NaCl (II), BaCl₂ (III) and urea (IV) have their osmotic pressure at the same temperature in the ascending order (molar masses of NaCl, KCl, BaCl₂ and urea are respectively 58.5, 74.5, 208.4 and 60 g.mol^-1). Assume 100% ionization of the electrolytes at this temperature.

• III < IV < I < II

• I < III < II < IV

• III < I < II < IV

• I < III < IV < II

The difference between the boiling point and freezing point of an aqueous solution containing sucrose (molecular wt = 342g mol^-1) in 100 g of water is 105.0°C. If k_f and k_b of water are 1.86 and 0.51 K kg mol^-1 respectively, the weight of sucrose in the solution is about?

• 34.2 g

• 342 g

• 7.2 g

• 72 g

The activation energies of two reactions are E₁ and E_{2 (}E₁ > E₂). If the temperature of the system is increased from T₁ to T₂, the rate constant of the reactions changes from k₁ to k${}_1^{\text{'}}$ in the first reaction and k₂ to k${}_2^{\text{'}}$ in the second reaction. Predict which of the following expression is

• $\frac{{\mathrm{k}}_1^{\text{'}}}{{\mathrm{k}}_1} = \frac{{\mathrm{k}}_2^{\text{'}}}{{\mathrm{k}}_2}$

• $\frac{{\mathrm{k}}_1^{\text{'}}}{{\mathrm{k}}_1} > \frac{{\mathrm{k}}_2^{\text{'}}}{{\mathrm{k}}_2}$

• $\frac{{\mathrm{k}}_1^{\text{'}}}{{\mathrm{k}}_1} < \frac{{\mathrm{k}}_2^{\text{'}}}{{\mathrm{k}}_2}$

• $\frac{{\mathrm{k}}_1^{\text{'}}}{{\mathrm{k}}_1} = \frac{{\mathrm{k}}_2^{\text{'}}}{{\mathrm{k}}_2}$

A reaction was observed for 15 days and the percentage of the reactant remaining after the days indicated was recorded in the following table

Which one of the following best describes the order and the half-life of the reaction?

• First - 2

• First - 6

• Second - 2

• Zero - 6

The ion that is more effective for the coagulation of As₂S₃ sol is

• Al³⁺

• Ba²⁺

• Na⁺

• SO${}_4^{2-}$

37.

Which one of the following impurities present in colloidal solution cannot be remove by electrodialysis ?

• Sodium chloride

• Potassium sulphate

• Urea

• Calcium chloride

Concentrated sulphuric acid can be reduced by

• NaCl

• NaF

• NaBr

• NaOH

The alkyl halide that undergoes S_N1 reaction more readily is

• t-butyl bromide

• n-propyl bromide

• vinyl bromide

• isopropyl bromide

An alkyl halide (R X) reacts with Na to form 4, 5-diethyloctane. Compound R X is

• CH₃(CH₂)₃Br

• CH₃(CH₂)₂CH(Br)CH₂CH₃

• CH₃(CH₂)₃CH(Br)CH₃

• CH₃(CH₂)₅Br