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Which of the following is used to produce smoke screens?A. CalciumB. Zinc sulphideC. Sodium carbonateD. Zinc phosphate

Answer» Correct Answer - A
Smoke screens are used in warfare for the purpose of concealment and camouflage.
`Ca_(3)P_(2)+6H_(2)Orarr3Ca(OH)_(2)+2PH_(3)`
Phosphine `(PH_(3))` so formed spontaneously catches fire to give `P_(2)O_(5)`
`2PH_(3)+4O_(2)rarrP_(2)O_(5)+3H_(2)O`
`P_(2)O_(5)` forms a white dense smoke screen. Very fine particles of titanium oxide dispersed in air are also used to create smoke screens. They are usually ejected from aeroplanes. As titanium oxide is very heavy, the smoke screen drops down rapidly as a curtain of dazzing whiteness.


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