This set of Chemistry MCQs for Class 12 focuses on “D and F-Block Elements – Transition Elements Compounds”.
1. What is the colour of KMnO4?
Explanation: The physical state of potassium permanganate (KMnO4) is an odourless solid, and they look like dark purple or bronze-coloured crystals. If we dissolve these crystals in water, then the solution becomes purple in colour.
2. What is the formula of hematite?
Explanation: Ferric oxide(Fe2O3) occurs in nature as haematite. It is a red powder, insoluble in H2O and not acted upon by air or H2O. It is amphoteric in nature and reacts with acids and alkalis and used as a catalyst in the oxidation of CO to CO2 in the Bosch process.
3. Mn has a maximum oxidation state of +6.
Explanation: The highest oxidation state in the oxides of any transition metal is equal to its group number, for example, 7 in Mn2O7. Beyond group 7, no higher oxides of iron above Fe2O3 are known. Some metals in higher oxidation state stabilize by forming oxocations.
4. Which of the following is amphoteric?
Explanation: Chromium(atomic no.24, symbol-Cr) forms many oxides. Some of its common oxidation states are +2, +3 and +6. Chromium (III) oxide (green in colour) is amphoteric, i.e., it can react as both acid and base. Its formula is Cr2O3.
5. Which of the following is Baeyer’sreagent?
a) Acidified KMnO4
b) Alkaline KMnO4
c) Acidified K2Cr2O7
d) Aqueous KMnO4
Explanation: Alkaline KMnO4 is called Baeyer’s reagent. Baeyer’s reagent is an alkaline solution of cold potassium permanganate, which is a powerful oxidant making this a redox reaction. Reaction with double or triple bonds (-C=C- or -C≡C-) in an organic material causes the colour to fade from purplish-pink to brown. It is a syn addition reaction.
6. Sc3+ is a paramagnetic ion.
Explanation: Scandium (atomic no.21, symbol-Sc) has the following electronic configuration:
In its Sc3+ state, scandium loses the 4s and 3d electrons and is colourless. Hence, Sc3+ is diamagnetic and not paramagnetic.
7. Which of the following metal is used as a thermometric liquid?
Explanation: Mercury (atomic no.80, symbol-Hg) is the only liquid metal at room temperature. It has a high coefficient of expansion and boiling point. This helps us to identify even the slightest change in temperature of the surroundings.
8. Which of the following tests does AgCl not answer?
a) Chromyl chloride test
b) Baeyer’s reagent test
c) Alkaline test
d) Acidic test
Explanation: Chromyl chloride test is done for detecting the presence of Cl– ions. The chlorides of silver, lead, mercury and antimony are covalent in nature and thus do not generate Cl– ions and so they do not give the chromyl chloride test also. So, heavy metal chlorides don’t give this test because they are not ionic.
9. Which compound forms double salt with sulphates of alkali metals?
a) Ferric oxide
b) Silver nitrate
c) Ferric chloride
d) Ferrous sulphate
Explanation: Ferrous sulphate forms double salts with sulphates of alkali metals with general formula R2SO4.FeSO4.6H2O. With ammonium sulphate, it forms a double salt known as Mohr’s salt. It ionises in solution to gives Fe2+, NH4+ and SO42- ions.
10. Which compound is used in Ultra-violet calibration?
Explanation: Potassium dichromate (K2Cr2O7) is especially useful in the visible range but also useful in UV. Potassium dichromate itself is stable and available in high purity. In dilute perchloric acid solution, it has a linear response with good temperature stability and also stable as solution.
Sanfoundry Global Education & Learning Series – Chemistry – Class 12.
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