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51.

The most reactive allotropic form of phosphorus is

A.	red phosphorus	B.	yellw phosphorus
C.	black phosphorus	D.	violet phosphorus

52.

The phosphorus vapours are composed of

A.	P	B.	P2
C.	P3	D.	P4

53.

Red phosphorus is chemically unreactive because

A.	it does not contain P-P bonds	B.	it does not contain tetrahedral P4 molecules
C.	it does not catch fire in air even upto 200?C	D.	it has a polymeric structure

54.

Red phosphorus may be changed to white phosphorus by

A.	vapourization followed by condensation	B.	heating in the presence of light
C.	heating under high pressure	D.	melting under pressure

55.

White phosphorus is most stable

A.	at ordinary temperature	B.	at atmospheric pressure
C.	above 600?C	D.	under high pressure

56.

Which of the following properties of white phosphorus are common to red phosphorus?

A.	It is soluble in carbon disulphide	B.	It phosphoresces in air
C.	It reacts with hot caustic soda solution to give phosphine	D.	It burns when heated in air

57.

Which of the following allotropic forms of phosphorus is used in the manufacture of safety matches?

A.	White phosphorus	B.	Red phosphorus
C.	Black phosphorus	D.	all forms of phosphorus

58.

Phosphate rock constitutes mainly of

A.	calcium phosphate	B.	calcium fluoride
C.	fluorapatite	D.	ammonium phosphate

59.

Phosporus is manufactured by heating in electric furnace a mixture of

A.	phosphate rock and coke	B.	phosphate rock and sand
C.	phosphate rock coke and sand	D.	phosphate rock coke and common salt

60.

Chemically bone ash is mainly

A.	calcium phosphate	B.	crude phosphorus
C.	animal charcoal	D.	ammonium phosphate