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The d & f Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe d & f Block Elements4 Marks
Question
Read the passage given below and answer the following questions:
Transition elements are elements that have partially filled d-orbitals. The configuration of these elements corresponds to $(n - 1)d^{1-10}ns^{1-2}.$ It is important to note that the elements mercury, cadmium and zinc are not considered transition elements because of their electronic configurations, which corresponds to $(n - 1)d^{10}ns^2.$ Some general properties of transition elements are:
These elements can fonn coloured compounds and ions due to $d-d$ transition;
These elements exhibit many oxidation states;
A large variety of ligands can bind themselves to these elements, due to this, a wide variety of stable complexes formed by these ions. The boiling and melting point of these elements are high. These elements have a large ratio of charge to the radius.
In these questions $(Q. No. i-iv),$ a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: Tungsten has very high melting point.
Reason: Tungsten is a covalent compound.
  1. Assertion: $Zn, Cd$ and $Hg$ are normally not considered transition metals.
Reason: d-Orbitals in $Zn, Cd$ and $Hg$ elements are completely filled, hence these metals do not show the general characteristics properties of the transition elements.
  1. Assertion: Copper metal gets readily corroded in acidic aqueous solution such as $HCl$ and dil. $H_2SO_4.$
Reason: Free energy change for this process is positive.
  1. Assertion: Tailing of mercury occurs on passing ozone through it.
Reason: Due to oxidation of mercury.
  1. Assertion: Transition metals are poor reducing agents.
Reason: Transition metals fonn numerous alloys with other metals.
✓

Answer

  1. (c) Assertion is correct statement but reason is wrong statement.
Explanation:

Tungsten is a transition element and is very hard due to high metallic bonding.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. (d) Assertion is wrong statement but reason is correct statement.
Explanation:

Non-oxidising acids $(HCl$ and dil. $H_2SO_4)$ do not have any effect on copper. However they dissolve the metal in presence of air. As it is a non-spontaneous process so, $\Delta\text{G}$ cannot be-ve.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
Explanation:

When mercury is exposed to ozone it gets superficially oxidised and loses its meniscus and sticks to the glass.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation:

In actual practice transition metals react with acid very slowly and act as poor reducing agents. This is due to the protection of metal as a result of formation of thin oxide protective film. Further, their poor tendency as reducing agent is due to high ionisation energy, high heat of vapourisation and low heat of hydration.

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