Chemical Reaction & Equations (Objectives)

 

 

Q.21. What type of chemical reactions take place when electricity is passed through water?
(a) Displacement
(b) Combination
(c) Decomposition
(d) Double displacement

Answer

Answer: c

Q.22.  When crystals of lead nitrate are heated strongly in a dry test tube     
(a)  crystals immediately melt
(b)  a brown residue is left     
(c)  white fumes appear in the tube
(d)  a yellow residue is left

Answer

Answer: b

Q.23. Which of the following is an endothermic process?
(a) Dilution of sulphuric acid
(b) Sublimation of dry ice
(c) Condensation of water vapours
(d) Respiration in human beings

Answer

Answer: b

Q.24.  Dilute hydrochloric acid is added to granulated zinc taken in a test tube. The following observations are recorded. Point out the correct observation.     
(a)  The surface of metal becomes shining     
(b)  The reaction mixture turns milky     
(c)  Odour of a pungent smelling gas is recorded     
(d)  A colourless and odourless gas is evolved

Answer

Answer: d

Q.25. When Ag is exposed to air it gets a black coating of
(a) AgNO₃
(b) Ag₂S
(c) Ag₂O
(d) Ag₂CO₃

Answer

Answer: b

Q.26. A substance ‘X’ is used in white-washing and is obtained by heating limestone in the absence of air. Identify ‘X’.
(a) CaOCl₂
(b) Ca (OH)₂
(c) CaO
(d) CaCO₃

Answer

Answer: a

Q.27.  When carbon dioxide is passed through lime water,     
(a)  calcium hydroxide is formed
(b)  white precipitate of CaO is formed     
(c)  lime water turns milky
(d)  colour of lime water disappears.

Answer

Answer: c

Q.28. Which of the following are exothermic processes?
(i) Reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Answer

Answer: a
Explanation: Reason: In both the cases, heat energy is evolved.

Q.29.  In which of the following, heat energy will be evolved?     
(a)  Electrolysis of water     
(b)  Dissolution of NH4Cl in water     
(c)  Burning of L.P.G.     
(d)  Decomposition of AgBr in the presence of sunlight

Answer

Answer: c

Q.30.  When a magnesium ribbon is burnt in air, the ash formed is     
(a)  black
(b)  white
(c)  yellow
(d)  pink

Answer

Answer: b