Free Combustion and Flame 01 Practice Test - 8th Grade
Question 1
Kerosene oil catches fire at room temperature.
SOLUTION
Solution : B
The lowest temperature at which a substance catches fire is its ignition temperature. The ignition temperature of kerosene is about 600C. Hence, it does not catch fire by itself at room temperature.
Question 2
Identify the appropriate category in which combustion can be categorised.
Physical process
Chemical process
Cyclic process
SOLUTION
Solution : B
Combustion refers to the process where a substance burns in the presence of oxygen, giving off heat and light in the process.
The way to recognize a chemical change is to check whether a new substance is being created or not. During combustion, the fuel reacts with oxygen to form some new gases. So, a new substance is definitely formed. So, combustion is a chemical change.
Question 3
Identify the correct option regarding the ignition temperature of an ideal fuel.
SOLUTION
Solution : B
Ignition temperature is the lowest temperature at which a substance catches fire. If the ignition temperature of a fuel is lower than the room temperature, then it can catch fire very easily.
Therefore for an ideal fuel, the ignition temperature should be higher than the room temperature.
Question 4
Given below is a sign that is seen on a box at a petrol filling station. What does this sign indicate?
SOLUTION
Solution : B
The given picture is a warning signal indicating that the substance kept inside the box is a inflammable substance. Substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. Examples of inflammable substances are petrol, diesel, LPG, etc.
Question 5
Smoke in a flame is due to the presence of carbon content in the fuel.
SOLUTION
Solution : B
Whenever there is some unburnt residue in the product gases, the particles diffuse light passing through them and we see it as smoke.
If oxygen supply is limited, it will result in unburnt suspended particles in product gases which do not get oxygen to react with. And when there are non-inflammable impurities, they too will not burn and will result in ash or suspended particles.
Question 6
The picture below shows two cases in which a person is trying to burn the paper cup. In case 1, the cup has water in it and in case 2, it is empty and dry. Identify in which of the cases the paper will burn.
Case 1
Case 2
Both case 1 and case 2
The paper doesn't burn in both the cases.
SOLUTION
Solution : B
In case 2, the empty paper cup reaches its ignition temperature and catches fire. In case 1, the heat supplied to the paper cup is transferred to water in it. So, in the presence of water, the ignition temperature of the paper is not reached. So, the paper would not burn in case 1.
Question 7
The suspended particles released by combustion of coal in air may lead to a health disease. Select the correct option.
Night Blindness
Asthma
Arthritis
Goitre
SOLUTION
Solution : B
Suspended particulate matter (SPM) refers to microscopic solid or liquid matter suspended in the Earth's atmosphere. Air pollutants consist of gaseous pollutants, odours, and SPM, (suspended particulate matter) such as dust, fumes, mist, and smoke. The high concentration of these in and near urban areas causes severe pollution to the surroundings. High amount of SPM in air leads to respiratory problems and lung related diseases like asthma.
Question 8
The usage of LPG in rural areas should be promoted because
it burns more easily than wood.
it is easily available in the village.
it has a higher calorific value than wood.
it is a cleaner fuel than wood.
SOLUTION
Solution : A, C, and D
A good fuel is one which burns easily, produces a large amount of heat and does not leave any undesirable substance.
For centuries, wood was used as domestic and industrial fuel. But now it has been replaced by fuels like LPG. In many rural parts, people still use wood as a fuel because of its easy availability and low cost. However, burning of wood gives a lot of smoke which is very harmful for human beings. It causes respiratory problem. Also calorific value of LPG (55000 KJ/Kg) is larger than the calorific value of wood (18000 KJ/Kg)
Question 9
White phosphorus burns in air spontaneously.
True
False
SOLUTION
Solution : A
White phosphorus is highly reactive and has a very low ignition temperature. It spontaneously ignites at about 30 °C in air. So if the room temperature is more than 30 °C, then it would catch fire.
It burns with a white flame producing clouds of white smoke. It is usually stored under water to prevent exposure to air.
Question 10
The colour of the outer zone of a candle flame is _________.
SOLUTION
Solution : D
The outer zone of candle flame is blue in colour. It is where the complete combustion takes place.
