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Showing 376 to 400 of 3046 questions (page 16 of 122).

376. Heisenberg's uncertainty principle states that the product of the uncertainties in position and momentum is

A. zero B. at least of the order of h/(4 pi) C. at most h D. equal to hf E. independent of h

377. The stopping potential in a photoelectric experiment depends on

A. the intensity of light only B. the frequency of light and the material C. the area of the cathode D. the distance of the source E. the polarization of light

378. According to Bohr's theory, the angular momentum of an electron in the nth orbit is

A. nh B. nh/(2 pi) C. h/(2 pi n) D. n2 h E. h/n

379. The spectral series of hydrogen that lies in the visible region is the

A. Lyman series B. Balmer series C. Paschen series D. Brackett series E. Pfund series

380. The ionization energy of a hydrogen atom in its ground state is

A. 3.4 eV B. 10.2 eV C. 13.6 eV D. 1.51 eV E. 27.2 eV

381. Laser action requires

A. thermal equilibrium B. population inversion C. a very low pumping rate D. incoherent sources E. a single energy level

382. The continuous part of an X-ray spectrum is produced by

A. electron transitions between inner shells B. deceleration of fast electrons in the target C. nuclear decay D. thermal emission from the filament E. stimulated emission

383. The radius of the nth Bohr orbit in hydrogen is proportional to

A. n B. n2 C. 1/n D. 1/n2 E. n3

384. Isotopes of an element have the same

A. mass number B. number of neutrons C. atomic number D. atomic mass E. binding energy

385. A radioactive sample has a half life of 10 days. The fraction remaining after 30 days is

A. 1/2 B. 1/4 C. 1/8 D. 1/16 E. 1/3

386. In beta minus decay, the atomic number of the nucleus

A. decreases by 1 B. increases by 1 C. decreases by 2 D. remains unchanged E. increases by 2

387. The energy released in nuclear reactions arises from

A. chemical bonding B. mass defect C. electron transitions D. frictional heating E. ionization

388. Energy production in the Sun is mainly due to

A. nuclear fission B. nuclear fusion C. chemical combustion D. radioactive decay of uranium E. gravitational contraction alone

389. Which radiation has the greatest penetrating power?

A. alpha B. beta C. gamma D. proton E. neutron in air only

390. In a nuclear reactor, the moderator is used to

A. absorb excess neutrons B. slow down fast neutrons C. shield the operators D. increase the fuel temperature E. control the coolant flow

391. The value of Avogadro's number is

A. 6.02 x 10^22 B. 6.02 x 10^23 C. 6.02 x 10^24 D. 3.01 x 10^23 E. 1.66 x 10^-24

392. The molar volume of an ideal gas at standard temperature and pressure is

A. 11.2 dm3 B. 22.414 dm3 C. 24 dm3 D. 1 dm3 E. 44.8 dm3

393. The reactant that is completely consumed first and therefore limits the amount of product is called the

A. excess reactant B. limiting reactant C. catalyst D. intermediate E. spectator species

394. A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is

A. CHO B. CH2O C. C2H4O2 D. CH4O E. C2H6O

395. The number of moles in 9.8 g of sulphuric acid is

A. 0.05 B. 0.1 C. 0.2 D. 1.0 E. 0.98

396. The number of molecules in 11.2 dm3 of oxygen gas at STP is

A. 6.02 x 10^23 B. 3.01 x 10^23 C. 1.204 x 10^24 D. 6.02 x 10^22 E. 1.5 x 10^23

397. Isotopes of an element are separated on the basis of

A. chemical reactivity B. difference in mass C. difference in colour D. difference in charge only E. boiling point of the compound

398. A fluted filter paper is used in filtration to

A. reduce the pore size B. increase the surface area available for filtration C. remove coloured impurities D. dry the precipitate E. neutralize the filtrate

399. Which pair of substances can be purified by sublimation?

A. sodium chloride and sugar B. iodine and naphthalene C. glucose and urea D. copper sulphate and alum E. ethanol and water

400. In paper chromatography, the Rf value of a component is always

A. greater than 1 B. equal to 1 C. less than or equal to 1 D. negative E. independent of the solvent

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