Hydrocarbons Test - 27

In the case of alkene, we have the order of stability as “ resonance>isolated>continuous pi bond”. The reason behind this is due to the presence of continuous Pi bond there is repulsion between the cloud of electrons and thus the alkene molecules with continuous pi bond become unstable. The heat of hydrogenation order is reverse the order of stability. We will find the stability. Due to resonance second is more stable than first. In three and four four is more stable as it has 6 Alpha hydrogen while 3  has only two Alpha hydrogen so the order of stability is  2>1>4>3, so the heat of hydrogenation order will be the reverse of this and the Order will be option number d

On addition of H₂/Pd/CaCO₃
we get H-CH=C-CH₂-CH₂-CH₃ 
H-CH=C-CH₂-CH₂-CH₃ + NBS/CCl₄   →   H-CH=C-CHCl-CH₂-CH₃  (NBS adds Br to carbon at next alternate to double bond)
H-CH=C-CHCl-CH₂-CH₃ + KOH/EtOH  →  H₂C=C-CH=CH-CH₃
(by E₂ elimination)

For option a
12 = [Ne]3s2 , 20 = [Ar]4s2 , 4 = [He]2s2 , 88 = [Ra]7s2.
For option b
8 = [He]2s22p4 , 16 = [Ne]3s23p4 , 34 = [Ar]4s23d104p4 , 2 = 1s2
We can see that only in option a, the last electrons enter in similar group. So, option a is correct.
Similarly we can check for option c and d as done above. However they won't fall in the same group.

The correct answer is option D
Diels - Alder reaction:

The correct answer is Option C.
A plane of symmetry is an imaginary plane that bisects a molecule into halves that are mirror images of each other.
A molecule has a center of symmetry when, for any atom in the molecule, an identical atom exists diametrically opposite this center an equal distance from it. In other words, a molecule has a center of symmetry when the points (x,y,z) and (−x,−y,−z) correspond to identical objects. For example, if there is an oxygen atom in some point (x,y,z), then there is an oxygen atom in the point (−x,−y,−z). There may or may not be an atom at the inversion center itself. Examples are xenon tetrafluoride where the inversion center is at the Xe atom, and benzene (C6H6) where the inversion center is at the center of the ring.
Optical activity is the ability of a chiral molecule to rotate the plane of plane-polarised light.