31.

A 250 W electric bulb of 80% efficiency emits a light of 6626 Å wavelength. The number of photons emitted per second by the lamp is (h = 6.636 x 10^-34 Js)

• 1.42 × 10¹⁷ 

• 2.18 × 10¹⁶ 

• 6.66 × 10²⁰ 

• 2.83 × 10¹⁶ 

The work function of a metal is 5 eV. What is the kinetic energy of the photoelectron ejected from the metal surface if the energy of the incident radiation is 6.2 eV? (1 eV = 1.6 × 10^-19)

• 1.92 × 10^-19 J

• 6.626 × 10^-19 J

• 8.10 × 10^-19 J

• 1.92 × 10^-18 J

The lattice energy of NaCl is 788 kJ mol^-1. This means that 788 kJ of energy is required

• to separate one mole of solid NaCl into one mole of Na (g) and one mole of Cl (g) to infinite distance

• to separate one mole of solid NaCl into one mole of Na⁺ (g) and one mole of Cl^- (g) to infinite distance

• to convert one mole of solid NaCl into one mole of gaseous NaCl

• to convert one mole of gaseous NaCl into one mole of solid NaCl

Which one of the following statements is not true in respect of propeties of interhalogen compounds?

• They are all covalent compounds

• They are volatile solids or liquids except ClF

• IF₅ has square pyramidal structure

• They are all paramagnetic in nature

An aqueous solution containing 3 g of a solute of molar mass 111.6 g mol^-1 in a certain mass of water freezes at -0.125°C. The mass of water in grams present in the solution is (K_f =1.86 K kg mol^-1)

• 300

• 600

• 500

• 400

The change in potential of the half-cell Cu²⁺|Cu when aqueous Cu²⁺ solution is diluted 100 times at 298 K? $\left(\frac{2.303 \mathrm{RT}}{\mathrm{F}} = 0.06\right)$

• increases by 120 mV

• decreases by 120 mV

• increases by 60 mV

• decreases by 60 mV

Consider the following elecrolytic cells

(i) M (s) | M²⁺ (aq), 0.1 M || X²⁺ (aq), 0.01 M | X (s)

(ii) M (s) | M²⁺ (aq), 0.1 M || X² (aq), 0.01 M | X (s)

(iii) M (s) | M²⁺ (aq), 0.1 M || X² (aq), 0.01 M | X (s)

The cell EMF of the above cells are E₁, E₂ and E₃ respectively. Which one of the following is true?

• E₃ > E₂ > E₁

• E₁ > E₂ > E₃

• E₂ > E₃ > E₁

• E₁ > E₃ > E₂

The correct decreasing order of reactivity for a given alkyl (R) group in both S_N1 and S_N2 reaction mechanisms is

• R - I > R - Br > R - Cl > R - F

• R - I > R - Cl > R - Br > R - F

• R - F > R - Cl > R - Br > R - I

• R - F > R - I > R - Cl > R - Br

The compound of molecular formula C₅H₁₀O(A) reacts with Tollen's reagent to give silver mirror but does not undergo aldol condensation. The compound A is

• 3-pentanone

• 2, 2-dimethylpropanal

• 3-hydroxy-2-pentene

• 3-methylbutanal

Chloroform reacts with oxygen in the presence of light to give

• carbon tetrachloride

• carbonyl chloride

• methyl chloride

• acetaldehyde