81.

The shortest wavelength of the line in hydrogen atomic spectrum of Lyman series when R_H = 109678 cm^-1 is

• 1002.7 Å

• 1215.67 Å

• 1127.30 Å

• 911.7 Å

Which of the following are isoelectronic species?

(i) NH₃

(ii) CH${}_3^{+}$

(iii) NH${}_2^{-}$

(iv) NH${}_4^{+}$

Choose the correct answer from the codes given below.

• (i), (ii), (iii)

• (ii), (iii), (iv)

• (i), (ii), (iv)

• (i), (iii), (iv)

The ratio of the frequency corresponding to the third line in Lyman series of hydrogen atomic spectrum to that of the first line in Balmer series of Li²⁺ spectrum is

• $\frac{4}{5}$

• $\frac{5}{4}$

• $\frac{4}{3}$

• $\frac{3}{4}$

Which transition in the hydrogen atomic spectrum will have the same wavelength as the transition will have the same wavelength, n = 4 to n = 2 of He⁺ spectrum?

• n = 4 to n = 3

• n = 2 to n = 1

• n = 4 to n = 2

• n = 3 to n = 1

The number of electrons, neutrons and protons in a species are equal to 10, 8 and 8 respectively. The proper symbol of the species

• ${}_8{}^{16}\mathrm{O}$

• ${}_8{}^{16}\mathrm{O}^{2-}$

• ${}_8{}^{16}\mathrm{O}^{-}$

• ${}_8{}^{18}\mathrm{O}$

A 600 W mercury lamp emits monochromatic radiation of wavelength 331.3 nm. How many photons are emitted from the lamp per second? (h = 6.626 x 10^-34 Js; velocity of light = 3×10⁸ ms^-1).

• 1 × 10¹⁹

• 1 × 10²²

• 1 × 10²¹

• 1 × 10²³

The shortest wavelength in hydrogen spectrum of Lyman series when R_H = 109678 cm^-1 is

• 1002.7 Å

• 1215.67 Å

• 1127.30 Å

• 911.7 Å

The electrons, identified by quantum numbers n and l,

(I) n = 3; l = 2; (II) n = 5; l = 0; (III) n = 4; l = 1; (IV) n = 4; l = 2; (V) n = 4; l = 0;

can be placed in order of increasing energy as-

• I < V < III < IV < II

• I < V < III < II < IV

• V < I < III < II < IV

• V < I < II < III < IV

The number of photons emitted per second by a 60 W source of monochromatic light of wavelength 663 nm is (h = 6 .63 × 10^-34 Js)

• 4 × 10^-20

• 1.5 × 10²⁰

• 3 × 10^-20

• 2 × 10²⁰

Energy released, when one atom of uranium undergoes nuclear fission according to the following reaction is (atomic mass of U = 235.060; n = 1.009; Ba= 143.881 and Kr = 89.94 7) about 

₉₂U²³⁵ + ₀n¹ → ₅₆Ba¹⁴⁴ + ₃₆Kr⁹⁰ + 2 ₀n¹

• 235 MeV

• 208 MeV

• 931.5 MeV

• 5.33 x 10²³ MeV