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NEET chemistry

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Question
CBSEENCH11008452
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With respect to the conformers of ethane, which of the following statements is true?

  • Bond angle remains same but bond length changes

  • Bond angle changes but bond length remains same

  • Both bond angle and bond length change

  • Both bond angles and bond length remains same

Solution

D.

Both bond angles and bond length remains same

There is no change in bond angles and bond lengths in the conformations of ethane. There is only change in dihedral angle.

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Question
CBSEENCH11008453
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Which of the following pairs of compounds is isoelectronic and isostructural?

  • BeCl2, XeF2

  • Tel2, XeF2

  • IBr2- , XeF 

  • IF3, XeF2

Solution

C.

IBr2- , XeF 

IBr2–, XeF2
The total number of valence electrons are equal in both the species and both the species are linear also.

Question
CBSEENCH11008454
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HgCl2 and I2 both when dissolved in water containing I– ions the pair of species formed is

  • HgI2 , I3-

  • Hgl2, I-

  • HgI43-, I3-

  • Hg2I2, I-

Solution

C.

HgI43-, I3-

In a solution containing HgCl2, I2 and I–, both HgCl2 and I2
compete for I–.
Since formation constant of [HgI4]2– is 1.9 × 1030
which is very large as compared with I3– (Kf= 700)
therefore, I– will preferentially combine with HgCl2
HgCl2 + 2l- → Hgl2↓ + 2Cl-
Hgl2 + 2l- → [Hgl4]2-

Question
CBSEENCH11008455
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Which one is the wrong statement?

  • de-Broglie's wavelength is given by λ = h/mv,
    where m = mass of the particle, v = group velocity of the particle

  • The uncertainty principle is increment straight E space straight x space increment straight t space greater or equal than space fraction numerator straight h over denominator 4 straight pi end fraction

  • Half-filled and fully filled orbitals have greater stability due to greater exchange energy, greater symmetry and more balanced arrangement

  • The energy of 2s orbital is less than the energy of 2p orbital in case of Hydrogen like atoms

Solution

D.

The energy of 2s orbital is less than the energy of 2p orbital in case of Hydrogen like atoms

Question
CBSEENCH11008456
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A gas is allowed to expand in a well-insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy ΔU of the gas in joules will be

  • 1136.5 J

  • -500 J

  • -505 J

  • +505 J

Solution

C.

-505 J

ΔU = q + w
For adiabatic process, q = 0
∴ ΔU = w
= – P·ΔV
= –2.5 atm × (4.5 – 2.5) L
= –2.5 × 2 L-atm
= –5 × 101.3 J
= –506.5 J
= –505 J

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