The substance used in smoke screen is :

• sodium chloride

• sodium phosphate

• calcium fluoride

• calcium phosphide

632.

Which of the following is the correct statement for PH₃?

• It is less poisonous than NH₃.

• It is less basic than NH₃.

• Electronegativity of PH₃ >NH_3.

• It does not show reducing properties.

HCl is a gas but HF is a low boiling liquid .This is because :

• H-F bond is strong

• H-F bond is weak

• molecules aggregate because of hydrogen bonding

• HF is a weak acid

Ostwald process is used for the manufacture of :

• nitric acid

• sulphuric acid

• ammonia

• bleaching powder

The chemical used for cooling in refrigerators is :

• CO₂

• NH₄OH

• NH₄Cl

• liquid NH₃

Which oxide of nitrogen is coloured gas ?

• N₂O

• NO₂

• N₂O₅

• NO

Which of the following inert gas liquifies easily ?

• He

• Kr

• Ne

• Ar

Which will not form precipitation after addition of (NH₄)₂CO₃ in presence of NH₄Cl?

• Mg

• Ba

• Sn

• Sr

Difference in atomic radius is maximum for

• Rb-Cs

• K-Rb

• Na-K

• Li-Na

Which is correct order of solubility in water?

• Ba(OH)₂ <Mg(OH)₂

• BaCO₃> CaCO₃

• CaSO₄ <MgSO₄

• Ca(OH)₂$\simeq$Mg(OH)₂