The rate constant of a reaction increases with increase in temperature. In general, the rate constant becomes almost double with rise in temperature by 10°.

(i) It is due to presence of unpaired electrons in d-orbitals therefore, they undergo d-d transitions by absorbing light from visible region and rediate complementary colour.
(ii) It is because neither Zn nor Zn²⁺ ion has incompletely filled d-orbital.

CuCl₂ is more stable due to more hydration energy.

(i) Compounds of transition elements are coloured due to the presence of incomplete d-subshell, i.e., unpaired electrons. These unpaired electrons gain energy and get excited to higher energy level and when they one come back, they radiate energy in vidible rang due to that from coloured compounds.
(ii) MnO is basic while Mn₂O₇ is acidic bacause the oxides in lower oxidation states of metals are basic and in their higher oxidation states, they are acidic.
\(M n O^{+2} M n_{2}^{+7} O_{7}\\ \underset{\text { (lower oxidation) }}{\operatorname{MnO}} and \underset{\text { (higher oxidation) }}{\operatorname{Mn}_{2} \mathrm{O}_{7}} idi\) 
\(\\ (b) Magnetic moment (\mu)=\sqrt{n(n+2)} B . M\) 
\(m(26)=1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{6}\) 
\(\\ M^{2+}=3 d^{6} (ion)\)

 Unpaid e−s = 4, i.e., n = 4 

μ = \( \sqrt{4(4+2)} \)
μ = \(\sqrt{24}\) = 4.90B.M

\({ Cr }^{ 2+ }\) is a stronger reducing agent than \({ Fe }^{ 2+ }\). This is because the configuration of \({ Cr }^{ 2+ }\) changes from \({ d }^{ 4 }\) to \({ d }^{ 3 }\) configuration is stable \(({ t }_{ 2g }^{ 3 })\) being half-filled \({ t }_{ 2g }\) level.

0.94 L mol^-1s^-1.

\(k={2.303\over t}log{[R]_0\over [R]}\)
\(={2.303\over 100}log{[R]_0\over {40\over 100}[R]_0}\)
[60% is complete, 40% is left]
\(k={2.303\over 100}(log5-log2)\)
\(k={2.303\over 100}(0.6990-0.3010)\)
\(k={2.303\over 100}\times0.3980\ min^{-1}\)
\(t_{90./.}={2.303\over k}log{[R]_0\over [R]}\)
[90% is complete, 10% is left]
\(t_{90./.}={2.303\over k}log{[R]_0\over {10\over 100}[R]_0}\)
\(={2.303\times100\over 2.303\times0.3980}log10\)
\(={100\over 0.3980}=251.26min\)

Temperature has a great effect on reaction rates or reaction rate constants. In general, an increase in temperature increases the rates of almost all reactions. For homogeneous chemical reactions, the rate of the reaction or rate constant (k) becomes almost double for every 10° rises in temperature.According to collision theory, the rate of reaction depends upon,
(i) the collision frequency of the reacting molecules.
(ii) the fraction of effective collisions.
The frequency of collisions between reacting molecules depends upon the average velocity of the molecules. With the increase in temperature, the average velocity of the molecules increases which results into increase in collision frequency. However, an increase of 10° rise of temperature increases the number of collisions by only 1.016 times. Further, we know that all the collisions are not effective. For molecules to undergo effective collisions, they must possess a certain minimum amount of energy called threshold energy. The molecules which possess energy equal to or greater than threshold energy will result in the formation of products. However, the fraction of such molecules capable of effective collisions is very small. As the temperature has increased the fraction of molecules possessing energies greater than threshold energy increases and so the rate of the reaction increases.
Let us consider the effect of increase of temperature on the number of effective collisions (having energies greater than threshold energy). The energy. distribution, of molecules at two temperatures \({ T }_{ 1 }\) and \({ T }_{ 2 }\) (where \({ T }_{ 2 }={ T }_{ 1 }+10°\)) is shown in figure. It is clear from the figure that the curve at higher temperature gets shifted towards the right indicating that at higher temperature, the molecules have higher energies. Further, the curve at higher temperature is flatter than that at lower temperature which also indicates that the number of molecules with higher energy content have increased.
The minimum energy required for the effective collisions also shown in the diagram and the number of molecules possessing energies equal to or greater than E, is proportional to area abed at temperature \({ T }_{ 1 }\) and area above at temperature \({ T }_{ 2 }\). In the figure, the area abef is roughly twice as large as abcd. Since the rate of reaction depends upon the number of molecules which possess energies larger than activation energy (for effective collisions), it may be interpreted that the fraction of molecules possessing activation energy has increased approximately two times and thereby, increases the rate of reaction by two times for a rise of 10 degrees.
Thus, we may conclude that increase in the rate of reaction with the rise in temperature is mainly due to the increase in number of effective collisions.

(i) Cu. This is because the electronic configuration of Cu is 3d10 4s1. After the loss of a 1st electron, it acquires stable configuration of 3dlO. Hence, removal of the 2nd electron is very difficult.
(ii) Zn. This is because Zn = 3dlO 4; and Zn2+ = 3d10 which is again fully filled and hence is very stable. Removal of 3rd electron requires very high energy.
(iii) Zn. This is because it has completely filled 3d subshell and no unpaired electron is available for metallic bonding.
(b) (i) Following EAN rule (page 9/102), M(CO)s is Fe(CO)s x -2
(ii) M03 p-l, X - 6 - 1 = 0, x = + 7, i.e., M is in oxidation state + 7. Mn shows an oxidation state of + 7. Hence, the compound is Mn03F.

(c) : For every 10^oC rise in temperature, rate constant is doubled, Hence, for 20^oC rise in temperature, rate constant will become 4 times, i.e., K₁ = 4 K₂ or K₂ = 0.25 K₁

(e) Assertion is incorrect but reason is correct. All collisions are never effective.

(b): The electronic configurations of europium (II) and cerium (II) are Eu²⁺ : [Xe] 4f⁷ and Ce²⁺ :
[Xe] 4f¹5d¹
In Eu²⁺,f - subshell is half-filled thus, it is more stable.

(i) (a) : 
 
(ii) (c) : The reaction proceeds with a constant rate which is independent of concentration of hydrogen and chlorine. That is why, this reaction is a zero order reaction.
(iii) (b) : For a zero order reaction   t_1/2 = [a]/2k. .
(iv) (a) :

(i) (b): The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states to form complexes.
(ii) (c) : Because of similar radii and other characteristics of transition metals, alloys are readily formed by these metals.
(iii) (c)
(iv) (b): Greater the number of valence electrons, more will be the number of oxidation states exhibited by the element.