Riya and her mom went to a goldsmith for getting some jewellery repaired. Goldsmith asked them to wait for some time while he repairs the jewellery. So, Riya and her mother were waiting in the shop.   

   

Riya observed that the goldsmith was blowing the outermost zone of the flame with a metallic blowpipe for melting gold and silver. Riya was curious to know the reason that why the outermost zone of the flame was being used. Can you explain the reason why?

                                      

Shwetabh saw a building catching fire when he was out with his uncle in a car. He immediately called the fire control room and informed them about the incident. A road curfew was imposed immediately to stop further movement on the road and prevent a stampede. After few minutes he saw that fireman were using a piece of equipment that helped the fire to extinguish. Most fire extinguishers are soda-acid extinguisher.

Could you help Shwetabh to know what chemical reaction takes place in a fire extinguisher if sodium bicarbonate and sulphuric acid are used as a reagent in it? What helps to extinguish fire?

Note: Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. It can be extinguished by cutting the oxygen supply to the fuel.

The teacher in a laboratory gave a task to her students in which they had to boil the water. Students were provided with a candle and beakers having the same volume of water. Rahul and Raju started heating the beaker.

a) Raju kept the water beaker near the wick in the yellow part of a candle flame.

 b) Rahul kept the water beaker in the outermost part of the flame. 

In which of the above situation's water will get boiled in a shorter time and why?

Oxygen is required for burning. But do all substances catch fire? To explain this, the chemistry teacher handed some substances to Tanya and asked her to light a matchstick on those substances.

Tanya has been provided with wood, paper, iron nail, straws, kerosene oil, sand, stone piece, charcoal and glass. Some of these substances could easily catch fire and some are resistant to fire.

Could you help Tanya make the categories of the two different types of substances? What are these substances called? Explain.

Aisha and Neel were coming back from school. They got shocked that their neighbour's house was caught on fire completely. In the meanwhile, a team of firefighters arrived at the location. They took their positions and started working.

But Aisha and Neel noticed that one of the firefighter rushed to put off the electric mains, while the other firefighters were taking their respective positions. Could you think of a reason why the firefighter did this?

Heating value is a very significant property of diesel fuels because it gives the energy content of the fuel. The heating value is expressed as a calorific value. The greater the calorific value the more efficient is the fuel. Calorific value is the heat produced on complete combustion of $1 \mathrm{kg}$ of fuel.

The calorific value of some common fuels are listed below:

Ritvik wants to understand that if he needs to get the same amount of energy from wood as much as he gets from  $1 \mathrm{kg}$ of petrol, does he need to burn $1 \mathrm{kg}$ of wood or he needs to increase its mass? Which fuel listed in the table above has the highest efficiency?

Hydrogen is considered clean fuel because its combustion unlike other fuels does not produce any harmful emissions. These harmful emissions are generally the oxides of non-metals which cause adverse effects on our environment. One such effect is global warming. Global warming is the state of rising the earth's temperature gradually. This temperature rise is due to the increased industrialisation and increased utilisation of automobiles over the last decade.

What does this graph suggest about the increment in earth's temperature by $1.5 °\mathrm{C}$? What is the major pollutant formed by the consumption of fuels that is responsible for global warming?

Write the combustion reaction for hydrogen to justify the fact that it is a clean fuel.

A teacher was explaining the experiments on the concept of 'material burns with or without a flame' in a laboratory. To demonstrate this experiment, the teacher gave a pine wooden cylinder wounded with paper and an aluminium cylinder wounded with paper to a group of students and instructed them to hold both cylinders over a Bunsen flame for ten seconds.

What happens when students hold both cylinders over a Bunsen flame, based on the above understanding? Explain your answer.

Sanju, a student in the eighth grade, attended a magic performance. The magician removes a piece of white solid from water during a magic trick. Immediately, it starts to burn. He has done this performance under highly protective conditions because the released gas is highly toxic. Sanju was perplexed since he knew that in order to burn something, a matchstick or lighter must be used, but in this instance, the magician used neither of them. Can you assist Sanju in determining the material and what we refer to as such substances that burst without apparent cause?