NECO Chemistry Past Questions & Answers - Page 5

21.

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.

22.

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.

23.

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.

24.

Atomic size decreases

A.

across a period from left to right

B.

across a period from right to left

C.

diagonally down the group

D.

down a group

E.

with decrease in atomic number

Correct answer is A

No explanation has been provided for this answer.

25.

Sulphur has an oxidation number of +4 in

A.

H2S

B.

H2S04

C.

MgSO4

D.

Na2SO3

E.

S03

Correct answer is D

No explanation has been provided for this answer.