NECO Past Questions and Answers - Page 79

391.

Which of the following metals is NOT extracted by electrolysis?

A.

Aluminium

B.

Calcium

C.

iron

D.

Magnesium

E.

Sodium

Correct answer is C

No explanation has been provided for this answer.

392.

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]

A.

0.32

B.

0.64

C.

3.18

D.

6.35

E.

9.65

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

393.

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

A.

2

B.

3

C.

4

D.

5

E.

6

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.

394.

When air is passed through alkaline pyrogallol and then lime water, the gases left are

A.

nitrogen and carbon (IV) oxide

B.

nitrogen and noble gases

C.

nitrogen and oxygen

D.

nitrogen, carbon (VI) oxide and noble gases

E.

the noble gases

Correct answer is B

No explanation has been provided for this answer.

395.

A salt which loses its mass when exposed to air is

A.

deliquescent

B.

effervescent

C.

Efflorescent

D.

fluorescent

E.

hygroscopic

Correct answer is C

No explanation has been provided for this answer.