NECO Past Questions and Answers

396.

Two elements X and Y with electronic configurations 2,8,2 and 2,8,7 respectively, are likely to combine by _________bonding

covalent

dative

electrovalent

hydrogen

metallic

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

397.

The furring of kettles and boilers are caused by

calcium hydroxide

calcium hydrogen trioxocarbonate (IV)

calcium trioxocarbonate (IV)

calcium tetraoxocarbonate

magnesium tetraoxocarbonate (VI)

View answer & explanation

Correct answer is C

The furring of kettles or boilers - this is as a result of the decomposition of Ca(HCO3)2 into CaCO3, and this coats the inside of a kettle or boiler used in heating water containing dissolved Ca(HCO3)2.

398.

Which of the following metals is NOT extracted by electrolysis?

Aluminium

Calcium

iron

Magnesium

Sodium

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

399.

What mass of copper in gram would be deposited by a current of 1.00ampere passing for 965 seconds through copper(II) tertraoxosulphate (VI) solution? [Cu 63.5; If = 96500c]

0.32

0.64

3.18

6.35

9.65

View answer & explanation

Correct answer is A

Recall that two faradays ( 2 X 96500 ) will be required to discharge 1 mole of a divalent ion like Cu.

2 X 96500 will deposit 63.5g of Cu

And 965C wiil deposit x-grams

CROSS MULTIPLY

(965 X 63.5) ÷ ( 2 X 96500)

= 0.3175

400.

How many zones are present in a luminous Bunsen burner flame?

View answer & explanation

Correct answer is C

The luminous bunsen burner flame has four zones namely:

Dark zone/ zone of unburnt gas; burning of the gas does not take place here, it is dark and cool.
Luminous yellow zone; the gas burns in this zone but not completely because of limited air. Tiny particles glow in this region to give out light.
Thin outer zone; the zone is colorless and gas burns completely due to plenty of air.
Blue zone; this zone receives plenty of air and burning is more complete than in the luminous zone.