JAMB Past Questions and Answers

7,931.

Addition of dilute hydrochloride acid to an aqueous solution of a crystalline salt yield a yellow precipitate and a gas which turned dichromate paper green. The crystalline salt was probably?

Na₂SO₄

Na₂S

Na₂S₂O₃.5H₂O

Na₂CO₃

NaHCO₃

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Correct answer is C

No explanation has been provided for this answer.

7,932.

When marble is heated to about 1473 K, another white solid is obtained which reacts vigorously with water to give an alkaline solution. The solution contains?

NaOH

KOH

Mg(OH)₂

Zn(OH)₂

Ca(OH)₂

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Correct answer is E

No explanation has been provided for this answer.

7,933.

The atomic number of an element whose cation, X2+, has the ground state electronic configuration 1s22s22p63s22p6 is?

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Correct answer is C

-The main difference between ground state and excited state is that ground state is a state where electrons in a system are in the lowest possible energy levels whereas excited state is any state of the system that has a higher energy than the ground state.

-Calcium atoms have 20 electrons and the shell structure is 2.8. 8.2. The ground state electron configuration of ground state gaseous neutral calcium is [Ar]

7,934.

Which of the following compounds is NOT the correct product formed when the parent metals is heated in air?

Calcium oxide (CaO)

Sodium oxide (Na₂O)

Copper (ll) oxide (CuO)

Tri-iron tetroxide (Fe₃O₄)

Aluminium oxide (Al₂O₃)

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Correct answer is D

No explanation has been provided for this answer.

7,935.

A colourless organic compound X was burnt in excess air to give two colourless and odourless gases, Y and Z, as products. X does not decolorize blue bromine vapour, Y turns lime milky while Z gives a blue colour with copper (ll) tetraoxosulphate (IV).
Y and Z are respectively?

CO₂ and NH₃

CO and NH₃

SO₂ and H₂O

CO₂ and H₂O

SO₂ and NH₃

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Correct answer is D

All saturated hydrocarbons are attacked by oxygen at elevated temperatures and, if oxygen is in excess, complete combustion to carbon dioxide and water occurs.