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

Which of the following statements is false?

• H₂  molecule has 1σ bond 

• Acetylene molecule has 3σ bonds and 3Π bonds

• HCl molecule has 1σ bond

• Water molecule has 2σ bonds and two lone pairs

N₂ and O₂ are converted to monopositive cation ${\mathrm{N}}_2^{+}$ and ${\mathrm{O}}_2^{+}$respectively. Which is incorrect?

• In ${\mathrm{N}}_2^{+}$, the N-N bond weakened.

• In ${\mathrm{O}}_2^{+},$ the bond order increases

• In ${\mathrm{O}}_2^{+},$ paramagnetism decreases

• ${\mathrm{N}}_2^{+}$  becomes diamagnetic

A netural molecule XF₃ has a zero dipole moment. The element X is most likely

• chlorine

• boron

• nitrogen

• carbon

56 g of nitrogen and 96 g of oxygen are mixed isothermally and at a total pressure of 10 atm. The partial pressures of oxygen and nitrogen (in atm) are respectively

• 6,4

• 4,6

• 5,5

• 2,8

How much time (in hours) would it take to distribute one Avogadro number of wheat grains, if 10²⁰ grains are distributed each second?

• 0.1673

• 1.673

• 16.73

• 167.3

The first () and second (ΔH₂) ionisation enthalpies (in kJ mol^-1) and the (Δ_egH) electron gain enthalpy (in kJ mol^-1) of the elements I, II, III, IV and V are given below

The most reactive metal and the least reactive non-metal of these are respectively

• I and IV

• IV and II

• II and IV

• III and IV

Calculate the standard enthalpy change (in kJ mol^-1) for the reaction

    H₂(g) + O₂(g) → H₂O₂(g)

Given that bond enthalpies of H-H, O=O, O-H and O-O (in KJ mol^-1) are respectively 438, 498, 464 and 138.

• -130

• -65

• +130

• -334