B. FILL IN THE BLANKS :
substances are formed.
1. In chemical change
2.
... burns with a dazzling white light.
3. ..
changes are reversible.
4. Chemical changes are accompanied by absorption or evolution of
Answers
Answer:
I know only 2 answer it is magnesium rod which burns with dazzling white flam
Answer:
Question 1:
Which of these is a chemical change?
(a) A substacne with different chemical properties is formed.
(b) A substance in a different state but similar chemical properties is formed.
(c) The molecules of the substances do not undergo any change.
(d) A substance with a different shape and size but similar chemical properties is formed.
ANSWER:
(a) A substance with different chemical properties is formed.
A chemical change occurs when two substances react chemically to form new substances with different chemical properties.
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Question 2:
Which of these is an irreversible physical change?
(a) rusting of iron
(b) freezing of water
(c) a double decomposition reaction
(d) breaking of a glass tumbler
ANSWER:
(d) breaking of a glass tumbler
Breaking of a glass tumbler is an irreversible physical change. Rusting of iron is a chemical change. Freezing of water is a reversible physical change. A double decomposition reaction is a chemical change.
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Question 3:
An arrow pointing downwards in a chemical reaction shows
(a) evolution of gas
(b) formation of precipitae
(c) oxidation
(d) displacement
ANSWER:
(b) formation of precipitate
In a chemical reaction, an arrow pointing downwards shows the formation of a precipitate and an arrow pointing upwards shows the evolution of a gas.
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Question 4:
A chemical reaction in which heat is given out is called
(a) exothermic reaction
(b) endothermic reaction
(c) decomposition reaction
(d) neutralization reaction
ANSWER:
(a) exothermic reaction
Exothermic reactions are accompanied with release of heat. Endothermic reactions are accompanied with absorption of heat.
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Question 5:
In a combination reaction how many products are formed?
(a) two only
(b) one or two only
(c) one only
(d) number cannot be specified
ANSWER:
(c) one only
In a combination reaction, a compound is formed from its elements. For example, water and oxygen combine to form water.
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Question 6:
What happens in a displacement reaction?
(a) A more reactive element replaces a less reactive element.
(b) A less reactive element replaces a more reactive element.
(c) An element replaces one which is equally reactive.
(d) Any element can replace any other element with no relation to reactivity.
ANSWER:
(a) A more reactive element replaces a less reactive element.
In a displacement reaction, a more reactive element replaces a less reactive element from its compound.
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Question 7:
A neutralization reaction is a
(a) decomposition reaction.
(b) displacement reaction.
(c) combination reaction.
(d) double displacement reaction.
ANSWER:
(d) double displacement reaction.
A neutralisation reaction is a double displacement reaction in which an acid reacts with a base, and the radicals are exchanged, to form salt and water.
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Question 8:
An oxidation reaction involves addition of
(a) oxygen only
(b) hydrogen only
(c) oxygen or removal of hydrogen
(d) hydrogen or removal of oxygen
ANSWER:
(c) oxygen or removal of hydrogen
An oxidation reaction involves addition of oxygen or removal of hydrogen from a substance.
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Question 9:
If which of the following reaction is there only one reactant?
(a) combination reaction
(b) decomposition reaction
(c) single displacement reaction
(d) double displacement reaction
ANSWER:
(b) decomposition reaction
In a decomposition reaction, a compound (reactant) breaks up into two or more substances (products).
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Question 10:
If A is more reactive than B, which of the following is true?
(a) A will replace B from a salt of B.
(b) B will replace A from a salt of A.
(c) Both can displace each other from their salts.
(d) Both cannot displace each other from their salts.
ANSWER:
(a) A will replace B from a salt of B.
The given reaction is an example of displacement reaction in which a more reactive element replaces a less reactive element from its salt solution.