Chemistry

(a) Fully filled and half-filled orbitals have extra stability (that is, lower energy). Thus, p³, p⁶, d⁵, d¹⁰, f ⁷, f¹⁴ etc. configurations, which are either half-filled or filled, are more stable. Chromium and copper therefore adopt the d⁵ and d¹⁰ configuration.

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It is a Wurtz reaction where alkane is formed.

(c) The path of an electron in an atom can never be determined or known accurately. That is why there is only a probability of finding the electron at different points in an atom.

This is a short answer type question as classified in NCERT Exemplar

The structure of 2-methylbutane is 

2-methylbutane

(a) Classical mechanics applies to the macro world and hence fails when it is applied to the micro world. In the micro world, quantum mechanics incorporates all the principles like the uncertainty principle, dual behaviour etc.

(d) Rainbow is a continuous spectrum.

Assertion is a wrong statement but Reason is a correct one. Rainbow is a continuous spectrum.

This is a short answer type question as classified in NCERT Exemplar

(a) For n = 4, No. of sub-shells = (l = 0, l = 1, l = 2, l = 3) = 4.

(b) Total number of orbitals which can be present = n² = 4² = 16.
Each orbital can have an electron with m_s = – 1/2. Total no. of electrons with m, = – 1/2 is 16.

This is a short answer type question as classified in NCERT Exemplar

In presence of (Ph-CO-O)₂it lead to CH₃-CH₂-CH₂Br as the reaction undergo by free radical mechanism

However in absence of (Ph-CO-O)₂ the reaction undergo by carbocation intermediate thus lead to give CH₃-CHBr-CH₃

(a) P (Z=15) : [Ne]¹⁰3s²3p³  No. of unpaired electrons = 3
(b) Si (Z=14) : [Ne]¹⁰3s²3p²  No. of unpaired electrons = 2
(c) Cr (Z=24): [Ar]¹⁸4s¹3d⁵  No. of unpaired electrons = 6
(d) Fe (Z=26): [Ar]¹⁸4s²3d⁶  No. of unpaired electrons = 4
(e) Kr (Z=36) : [Ar]¹⁸4s²3d¹⁰4p⁶  No. of unpaired electrons = Nil.