Chemistry
Assertion (A): For rust formation to take place, iron must be exposed to air and water for some time.
Reason (R): Rust is a reddish brown substance formed on the surface of iron.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false
- A is false but R is true.
Phy & Chem Changes
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Answer
Both A and R are true but R is not the correct explanation of A.
Explanation — Assertion is correct, iron rusts only when both oxygen (air) and water are present for some time. The Reason is also true, rust is a reddish-brown substance (hydrated iron(III) oxide). However, R just describes rust; it does not explain why air and water are needed for rusting.
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Related Questions
Assertion (A): When a change in a substance can be reversed by changing the conditions, it is said to be a reversible and temporary change.
Reason (R): Burning a piece of paper is a reversible change.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false
- A is false but R is true.
Assertion (A): Sublimation of camphor is a physical change.
Reason (R): No new substance is formed.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false
- A is false but R is true.
Assertion (A): Burning of a candle is a physical change.
Reason (R): When a candle burns, some of its wax melts and gets solidified on cooling. Also carbon dioxide and water vapour are formed which cannot be recovered easily and converted back into the candle.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false
- A is false but R is true.
Fill in the blanks:
(a) The process of a liquid changing into a solid is called …………… .
(b) A change which alters the composition of a substance is known as a …………… change.
(c) There is no change in the …………… of the substance during a physical change.
(d) The reaction in which energy is evolved is called …………… .
(e) The process in which a substance in solid state directly changes into ............... is called sublimation.