Variable oxidation numbers are possible for :
- A.Sodium
- B.Calcium
- C.Iron
- D.Lithium
Correct answer
Explanation
The correct answer is C, Iron. Iron is a transition (d-block) element, and such elements can show more than one oxidation state.
In transition metals the energies of the outer s electrons and the inner d electrons are very close, so atoms can lose different numbers of electrons. Iron commonly shows +2 (ferrous, as in FeSO₄) and +3 (ferric, as in Fe₂O₃ and FeCl₃). This is also why many iron compounds are coloured and why rust contains iron in the +3 state.
A is wrong: sodium is an alkali metal with one valence electron and shows only +1.
B is wrong: calcium is an alkaline earth metal with two valence electrons and shows only +2.
D is wrong: lithium is also an alkali metal and shows only +1 in its compounds.
Exam tip: s-block metals have a fixed oxidation state (group 1 = +1, group 2 = +2); d-block metals like Fe, Cu and Mn show variable states (Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺).
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
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