19. A fuel used in spacecraft
a. Diesel b. Hydrogen c. Petrol d. Coal
20. Ignition temperature of red phosphorous is
a. 65 °C b. 45 °C c. 35 °C d. 260 °C
21. The protein synthesizing organelles in the cell are
a. Mitochondria b. Golgi bodies c. Vacuole d. Ribosomes
22. Which of the following is the powerhouse of a cell?
a. Mitochondria b. Golgi bodies c. Vacuole d. Ribosomes
23. The organelle which helps in manufacture of food in plants is
a. Chloroplast b. Golgi bodies c. Vacuole d. Ribosomes
24. Which of the following structures is not present in all cells?
a. Cell membrane b. Cytoplasm c. Nucleus d. Plastids
25. Cells without a nucleus are called
a. Unicellular b. Multicellular c. Enucleated cells d. Eukaryotes
Q-2 Answer in one word (5×1=5)
1. Write the SI unit of pressure.
2. What are disease causing microorganisms called?
3. Which is the least hot region of the candle flame?
4. Name the metal which is liquid at room temperature.
5. Who discovered the cell?
Answers
Answer:
People generally use wood, cowdung cakes, crop residues, kerosene oil, coke or LPG gas to cook food. For ruining vehicles, we use petrol or diesel oil. In factories, we use coal or fuel oil or natural gas.
The materials, such as wood, coke, LPG (liquid petroleum gas), petrol, diesel, natural gas have one property [n common, i.e., they produce heat on burning which is then put into different uses. Furthermore, some materials on burning produce flame and some do not. For example, a candle or coal gas on burning produces a flame, but not the coal or charcoal. So, let us study the chemical process of burning and the types of flame produced during this process.
Combustion
Some substances, like magnesium catches fire and burns with a dazzling white flame when heated in air. Similarly, when a piece of per is brought near a candle flame, it burns, producing heat and light. The charcoal and coal bums in air producing carbon dioxide, heat and light.
Air or oxygen which helps in burning is called supporter of combustion and the chemical reaction which takes place with the release of heat and light energy is called combustion.
A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
The substances which undergo combustion are known as combustible substances. It may also be called a fuel.
Sometimes, heat is accompanied by light, either as a flame or as a glow, during combustion.
Fuel may be solid, liquid or gas. A combustion reaction maybe written as-
(a) Charcoal burns in air to give carbon dioxide and heat.
C + O2 → CO2 + Heat
(b) Methane bums in air forming carbon dioxide, water and heat.
CH4 + 2O2 → CO2 + 2H2O + Heat
Explanation:
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Answer:
19. Hydrogen
20. 260°C
21. Ribosome
22. Mitochondria
23. Chloroplast
24. plastids
25. Enucleated cells
Q-2
1. Pascal
2. Pathogen
3. Innermost
4. Mercury
5. Robert Hooke
Explanation:
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