CBSE Class 7 Science Advanced Chemistry Air and Oxygen Very Short Answer Questions Set 03

Very Short Answer Questions

Question 1. \(\ce{CO2}\) can be used to preserve food grains from destruction by insects.
Answer:
True. Insects cannot live in an atmosphere of carbon dioxide.
In simple words: Carbon dioxide protects stored grains.

Teacher's Note:
1. Check the statement against the facts in the notes.
2. If a statement is false, always correct it to see why.

Question 2. \(\ce{CO2}\) can be collected by the downward displacement of air.
Answer:
False. \(\ce{CO2}\) is heavier than air, so it is collected by upward displacement of air.
In simple words: A heavy gas settles at the bottom, so air is pushed up and out.

Teacher's Note:
1. Check the statement against the facts in the notes.
2. If a statement is false, always correct it to see why.

Question 3. The electric spark produced during lightening helps nitrogen to combine with oxygen to form nitric oxide.
Answer:
True. The energy of lightning makes \(\ce{N2}\) and \(\ce{O2}\) combine: \(\ce{N2 + O2 -> 2NO}\).
In simple words: Lightning gives the energy that joins nitrogen with oxygen.

Teacher's Note:
1. Check the statement against the facts in the notes.
2. If a statement is false, always correct it to see why.

Question 4. Carbogen is a mixture of 94% oxygen, 4% carbon dioxide and 2% nitrogen dioxide.
Answer:
False. Carbogen is a mixture of 95% oxygen and 5% carbon dioxide.
In simple words: Carbogen contains only oxygen and carbon dioxide, in the ratio 95 : 5.

Teacher's Note:
1. Check the statement against the facts in the notes.
2. If a statement is false, always correct it to see why.

Question 5. Dust particles along with water vapour present in the atmosphere help in the formation of clouds.
Answer:
True. Water vapour condenses on dust particles to form tiny droplets, which make clouds.
In simple words: Dust gives water vapour something to condense on.

Teacher's Note:
1. Check the statement against the facts in the notes.
2. If a statement is false, always correct it to see why.

Question 6. ______ is present in sun's atmosphere up to 1.1%.
Answer:
Hydrogen.
In simple words: Hydrogen is found in the sun's atmosphere.

Teacher's Note:
1. Free hydrogen is rare on the earth, but plentiful in the sun.
2. Learn such facts as one-line pairs for quick revision.

Question 7. ______ is used as catalyst in the hydrogenation of oils.
Answer:
Nickel.
In simple words: Nickel is the catalyst used to harden oils.

Teacher's Note:
1. Hydrogenation turns liquid vegetable oil into vanaspati.
2. Learn such facts as one-line pairs for quick revision.

Question 8. Composition of water gas is _________
Answer:
\(\ce{CO + H2}\) (carbon monoxide and hydrogen).
In simple words: Water gas is carbon monoxide mixed with hydrogen.

Teacher's Note:
1. It is made by passing steam over red-hot coke.
2. Learn such facts as one-line pairs for quick revision.

Question 9. _______ is used as a rocket fuel.
Answer:
Liquid hydrogen.
In simple words: Liquid hydrogen is a rocket fuel.

Teacher's Note:
1. Liquid oxygen is used along with it as the supporter of combustion.
2. Learn such facts as one-line pairs for quick revision.

Question 10. Oxygen is _______ towards litmus.
Answer:
Neutral.
In simple words: Oxygen does not change litmus.

Teacher's Note:
1. It neither turns blue litmus red nor red litmus blue.
2. Learn such facts as one-line pairs for quick revision.

Question 11. Chemical formula of white lead is ________.
Answer:
\(\ce{Pb(OH)2.PbCO3}\).
In simple words: White lead is a basic carbonate of lead.

Teacher's Note:
1. Carbon dioxide is used in its manufacture.
2. Learn such facts as one-line pairs for quick revision.

Question 12. The atmospheric pressure is maximum at _____ and is found to be equal to _______.
Answer:
Maximum at sea level; it equals 760 mm of Hg (1 atm).
In simple words: Pressure is greatest at sea level, 760 mm of mercury.

Teacher's Note:
1. Pressure falls as we go to greater heights.
2. Learn such facts as one-line pairs for quick revision.

Question 13. In _____ layer of atmosphere TV waves do not get reflected. Hence artificial satellites are used for television transmission.
Answer:
Ionosphere (thermosphere).
In simple words: TV waves pass through the ionosphere, so satellites relay them.

Teacher's Note:
1. Radio waves, on the other hand, are reflected by this layer.
2. Learn such facts as one-line pairs for quick revision.

Question 14. Nascent hydrogen is a strong _______ agent. (reducing/oxidizing)
Answer:
Reducing agent.
In simple words: Nascent hydrogen takes away oxygen and reduces substances.

Teacher's Note:
1. It is freshly formed hydrogen, written [H].
2. Learn such facts as one-line pairs for quick revision.

Question 15. ______ is used for burning fuel in rockets and space ships.
Answer:
Liquid oxygen.
In simple words: Liquid oxygen helps to burn the rocket fuel.

Teacher's Note:
1. Oxygen is the supporter of combustion.
2. Learn such facts as one-line pairs for quick revision.

Teacher's Note:
1. Use the table of pollutants and their effects in the notes.
2. One pollutant can have more than one effect.

Teacher's Note:
1. Some items in column A match two entries.
2. Kipp's apparatus is used to make hydrogen, from which nascent hydrogen is obtained.

Teacher's Note:
1. Acidic oxides on dissolving in water give acids.
2. Notice that \(\ce{NO2}\) gives two acids at once.