Electron affinity is positive when from Chemistry Structure of A

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 Multiple Choice QuestionsMultiple Choice Questions

171.

A proton is converted to a neutron by

1.β- emission

2.β+ emission

3. electron capture

Which of the statements given above are correct?

  • (1) and (2) only 

  • (2) and (3) only

  • (1) and (3) only

  • (1), (2) and (3)


172.

In Neptunium series

Pu94241AmNpPaU92238, the order of radiation

  • β,α,α,β

  • β,β,α,α

  • α,α,β,β

  • α,β,α,β


173.

What number of subshells are possible in n = 3 energy level?

  • 7

  • 8

  • 9

  • 6


174.

Four different sets of quantum numbers for 4 electrons are given below:

e1 = 4, 0, 0, -12

e2 = 3, 1, 1, -12

e3 = 3, 2, 2, +12

e4 = 3, 0, 0, +12

The order of energy of e1, e2, e3, e4 is 

  • e> e> e> e4

  • e> e> e> e1

  • e> e> e> e4

  • e> e> e> e1


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175.

Which of the following nuclei is most unstable?

  • Ca2040

  • Mn3555

  • Sn50119

  • Al1330


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176.

Electron affinity is positive when

  • O- is formed from O

  • O2- is formed from O-

  • O+ is formed from O

  • electron affinite is always a negative value


B.

O2- is formed from O-

Electron affinity of an element is equal to the energy released when an electron is added to valence shell of an isolated gaseous atoms. For example, when an electron is added to oxygen atom to form O- ion, energy is released, i.e., EA1, value is exoergic or negative.

O (g) + e- (g)  O- (g)

H (EA1) = -141 kJ mol-1  (Energy is released)

But the addition of second electron to O- ion to form O2- ion is more difficult and energy is needed to overpower the repulsion forces between negatively charged atomic sphere and test electrons. Thus, the EA2 value of oxygen atom is positive or endoergic.

O- (g) + e- (g)  O2- (g)

H (EA2) = +780 kJ mol-1  (Energy is abosorbed)

Thus, the EA1 values for all elements are exoergic (however for some elements endoergic, e.g. noble gases and alkali earth metals) while rest all (EA2, EA3 ....) endoergic.


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177.

A particle 'A' moving with a certain velocity has the de-Broglie wavelength 1 Å. For a particle 'B' with mass 25% of 'A' and velocity 75% of 'A'. The de-Broglie wave length of 'B' will be

  • 3 Å

  • 5.33 Å

  • 6.88 Å

  • 0.68 Å


178.

The ratio of de-Broglie wavelengths for electron accelerated through 200 V and 50 V is

  • 1:2

  • 2:1

  • 3:10

  • 10:3


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179.

The nuclear reaction, Al1327 + He24  Si1430 + H11 is

  • nuclear fusion

  • nuclear fission

  • nuclear transmutation

  • artificial radioactivity


180.

n/p ratio during positron decay

  • increases

  • decreases

  • remains constant

  • All of these


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