For question numbers (i) and (ii) two statements are given one labelled as Assertion (A)and the other labelled as Reason (R) select the correct answer to these questions from the codes (a), (b),(c) and (d) are given below.
- Both assertion (A) and reason are true and Reason (R) is the correct explanation of the assertation (A)
- Both assertion (A) and reason are true and Reason (R) is not the correct explanation of the assertation (A)
- Assertion (A) is true but reason (R) is false
- Assertion (A) is false, (R) is true. A and R are true and (R) is the correct explanation of the assertation
- Both A and R are true, but R is not the correct explanation of the assertion.
- A is true, but R is false.
- A is false, but R is true.
(i) Assertion (A): Iron articles are coated with zinc.
Reason (R): The layer of zinc prevents the iron from rusting.
(ii)Assertion (A): Chemical change involves the formation of a new substance.
Reason (R): Composition of matter changes during a physical change while it remains the same during a chemical change
(i)Assertion (A): Iron articles are coated with zinc. Reason (R): The layer of zinc prevents the iron from rusting.
Answer: (a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Explanation: Coating iron articles with zinc (a process known as galvanization) prevents rusting because the zinc layer acts as a protective barrier against moisture and oxygen.
Assertion (A): Chemical change involves the formation of a new substance. Reason (R): Composition of matter changes during a physical change while it remains the same during a chemical change.
Answer: (c) Assertion (A) is true, but Reason (R) is false.
Explanation: Assertion (A) is true because a chemical change does involve the formation of a new substance. However, Reason (R) is false because the composition of matter changes during a chemical change, not a physical change. In a physical change, the composition of matter remains the same.
Q3. Answer the following questions in one sentence.
- What is change?
Answer. Change is the process through which something becomes different in some way.
- What factors can bring about change in matter?
Answer. Factors such as temperature, pressure, chemical reactions, and physical forces can bring about change in matter.
- What is crystal?
Answer. A crystal is a solid material whose atoms are arranged in a highly ordered, repeating pattern extending in all three spatial dimensions.
- What is galvanisation?
Answer. Galvanization is the process of coating iron or steel with a layer of zinc to prevent rusting.
Q4. Answer the following questions in 23 sentences
- Why is the burning of wax considered to be a chemical change?
Answer. The burning of wax is considered a chemical change because it involves a chemical reaction where the wax (hydrocarbon) reacts with oxygen to produce new substances, such as carbon dioxide, water vapor, and heat. This process is irreversible, and the original wax cannot be recovered.
- Explain with an example what is a reversible change.
Answer. A reversible change is a change that can be undone, returning the substance to its original state. An example is the melting of ice into water; when water is frozen again, it returns to its original solid state as ice.
- What is acidity? Why milk of magnesia is used to treat acidity?
Answer. Acidity is the condition of having excess stomach acid, which can cause discomfort and indigestion. Milk of magnesia is used to treat acidity because it is a mild base (magnesium hydroxide) that neutralizes the excess stomach acid, providing relief from symptoms.
Q5. Answer the following question in 34 sentences
a. Explain how digestion is both a physical and chemical change.
Answer.Digestion is a physical change because food is broken down into smaller pieces through chewing and the churning action in the stomach, which increases the surface area for enzymes to work on. It is also a chemical change because enzymes and acids in the digestive system chemically break down complex molecules like proteins, carbohydrates, and fats into simpler substances such as amino acids, sugars, and fatty acids that can be absorbed by the body.
b. What is an alloy? Give two examples of alloys.
Answer.An alloy is a mixture of two or more elements, where at least one is a metal, that combines the properties of the constituent elements to create a material with enhanced characteristics. Two examples of alloys are:
1. Steel: An alloy of iron and carbon, often with other elements like chromium or nickel, known for its strength and durability.
2. Brass: An alloy of copper and zinc, known for its corrosion resistance and attractive appearance.
c. Explain what is a precipitation reaction with the help of an example.
Answer.A precipitation reaction occurs when two aqueous solutions react to form an insoluble solid, called a precipitate, which separates from the solution. An example is the reaction between aqueous solutions of silver nitrate (AgNO₃) and sodium chloride (NaCl), which produces solid silver chloride (AgCl) as a precipitate and aqueous sodium nitrate (NaNO₃):
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).