21.

Which of the following conditions is not correct for resonating structures?

• The contributing structures must have the same number of unpaired electrons.

• The contributing structures should have similar energies.

• The contributing structures should be so written that unlike charges reside on atoms that are far apart.

• The positive charge should be present on the electropositive element and the negative charge on the electronegative element.

Degree of unsaturation of A= 2 double or triple bond. Identify A.

• 

• 

• 

• None of these 

Which of the following acids will not evolve H₂ gas on reaction with alkali metals?

• Hydrazoic acid

• Perxenic acid

• Boric acid

• None of these

Which is optically inactive?

Assertion : The nuclear isomers are the atoms with the same atomic number and same mass number, but with different radioactive properties.

Reason : The nucleus in the excited state will evidently have a different half-life as compared to that in the ground state

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion : Conductivity of silicon increases by doping it with group-15 elements.

Reason : Doping means introduction of small amount of impurities like P, As or Bi into the pure crystal.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion : 2,3-Dimethylbut-2-ene is more stable than but-2-ene.

Reason : Six hyperconjugation structures can be written for 2, 3-dimethylbut-2-ene while but-2-ene has twelve.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Butter is an example of which type of colloid?

• Solid in liquid

• Liquid in solid

• Liquid in liquid

• Gas in liquid

What are constituents of 'Mischmetal'?

• La, Fe

• La, Ce

• Fe, Ce

• Ce, Cu

For a 1^st order reaction if concentration is doubled then rate of reaction becomes

• doubles

• half

• four times

• remains same