NCERT Solutions For Class 6 Science Chapter 6

CBSE All In One SCIENCE Class 6

6 Science Chapter 6 Important Questions For Practice

1. Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim
(a) expands and fits onto the wooden wheel.
(b) contracts and fits onto the wooden wheel.
(c) no change in the size takes place.
(d) expands first, then on cooling contracts and fits onto the wooden wheel.
2. An iron ring is heated. Which of the following statement about it is incorrect?
(a) The ring expands.
(b) The ring almost comes to the same size on cooling.
(c) The change in this case is reversed.
(d) The ring changes its shape and the change cannot be reversed.
3. Pick the change that can be reversed from the following
(a) Cutting of trees
(b) Melting of ghee
(c) Burning of candle
(d) Blooming of flower
4. While lighting a candle, Paheli observed the following changes
(i) Wax was melting.
(ii) Candle was burning.
(iii) Size of the candle was reducing.
(iv) Melted wax was getting solidified.
5. Rolling of chapati and baking of chapati are the changes that
(a) can be reversed.
(b) cannot be reversed.
(c) can be reversed and cannot be reversed, respectively.
(d) cannot be reversed and can be reversed, respectively.
6. Which of the following change cannot be reversed?
(a) Hardening of cement (b) Freezing of ice cream (c) Opening a door (d) Melting of chocolate
7. Salt can be separated from its solution (salt dissolved in water), because
(a) mixing of salt in water is a change that can be reversed by heating and melting of salt.
(b) mixing of salt in water is a change that cannot be reversed.
(c) mixing of salt in water is a permanent change.
(d) mixing of salt in water is a change that can be reversed by evaporation.

Answers Of Important Questions

1 (d),
2 (d),
3 (b),
4 (d),
5 (c),
6 (a),
7 (d).

Important Questions On Class 6 Science Chapter 6

To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

Yes, by unfolding the dress this change can be reversed.

अकस्मात आपका प्रिय खिलौना गिरकर टूट जाता है। आप कतई इस परिवर्तन को नहीं चाहते थे। क्या यह परिवर्तन उत्क्रमित किया जा सकता है?

नहीं, इसे उत्क्रमित नहीं किया जा सकता है।

चित्रकारी करने पर ड्राइंग शीट में परिवर्तन हो जाता है। क्या आप इस परिवर्तन को उत्क्रमित कर सकते हैं?

यह सब परिस्थितियों पर निर्भर करता है:
ड्राइंग को मिटाकर हम परिवर्तन को पूर्ववत कर सकते हैं। उदाहरण के लिए, यदि हम चित्रकारी पेंसिल की मदद से करते हैं, तो हम रबर का प्रयोग करके उसको मिटा सकते हैं। फिर, यह एक उत्क्रमित परिवर्तन है।
यदि हम एक पेन का उपयोग करते हैं, तो हम ड्राइंग को मिटा नहीं सकते हैं। तब, यह उत्क्रमित परिवर्तन नहीं है।

Give examples to explain the difference between changes that can or cannot be reversed.

Examples of Reversible Changes:
Melting of Ice into water. By freezing the water we can obtain ice again.
Folding a paper: By unfolding it, we can undo the change.
Hot milk to cold milk: By boiling milk, we can make it warm.
Example of Irreversible Changes:
Burning of candle.
Bursting of crackers.
Cutting of trees.

A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

When water is added to POP, it undergoes a chemical change. Its composition changes and is converted into another substance. Since it is a chemical change, so it cannot be reversed.

रात्रि में एक सीमेंट की बोरी जो कि खुले मैदान में रखी हुई थी, वर्षा के कारण भीग जाती है। अगले दिन तेज धूप निकलती है। सीमेंट में जो परिवर्तन हो गया है क्या उसे उत्क्रमित कर सकते हैं?

पानी के कारण, सीमेंट में रासायनिक क्रिया होती है और यह कठोर हो जाता है तथा इसकी संरचना बदल जाती है। चूंकि यह एक रासायनिक परिवर्तन है, अतः इसे उत्क्रमित नहीं किया जा सकता है।

Details: Parent Category: student Corner; Category: Class 6 Science; Published: 18 May 2020; Hits: 55

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Class 6 Science