Which of the following statements are true for the reaction of Fe2O3 with aluminium? 1. It is known as the 'thermite reaction'. 2. The heat evolved is used for welding purpose. 3. Aluminium metal acts as an oxidizing agent. 4. Molten Fe and Al are formed at the end of the reaction. Select the correct answer using the code given below.
- A.1 and 2
- B.1 and 3
- C.2 and 4
- D.1 and 4
Correct answer
Explanation
The correct answer is A, 1 and 2. When iron(III) oxide is heated with aluminium powder, aluminium takes away the oxygen, and the reaction gives out so much heat that the iron produced is molten: Fe2O3 + 2Al → 2Fe + Al2O3 + heat. This is the thermite reaction, so statement 1 is correct. The molten iron is used to join railway tracks and to weld cracked machine parts, so statement 2 is correct. Statement 3 is wrong because aluminium is the reducing agent: it removes oxygen from Fe2O3 and is itself oxidised to aluminium oxide, while Fe2O3 is the oxidising agent. Statement 4 is wrong because the products are molten iron and aluminium oxide, not molten aluminium; the aluminium is used up in the reaction. Option B is wrong because it includes statement 3. Option C is wrong because it includes statement 4 and leaves out statement 1. Option D is wrong because it includes statement 4. Exam tip: in the thermite reaction aluminium is the reducing agent, and the molten iron welds railway tracks.
Practice Questions
View allIn the joining of railway tracks, iron oxide is made to react with
- A.Aluminium
- B.Zinc
- C.Copper
- D.Tin
Show answer
Railway tracks are joined by the thermite process, in which aluminium powder reduces iron oxide to molten iron. The reaction is Fe₂O₃ + 2Al → 2Fe + Al₂O₃.
Read the full explanation →If atomic number of an element is 11, the correct name, symbol and valency are :
- A.Lithium, Li, 1
- B.Magnesium, Mg, 2
- C.Boron, B, 3
- D.Sodium, Na, 1
Show answer
The element with atomic number 11 is sodium, and with one electron in its outermost shell its valency is 1.
Read the full explanation →A car of mass 800 kg is travelling at a speed of 40 km/h on a straight road. A force of 1000 N is applied on it in the direction of its velocity for 12 s. Which one among the following is the final speed of the car?
- A.55 km/h
- B.60 km/h
- C.94 km/h
- D.104 km/h
Show answer
The force gives the car an extra 15 m/s, which is 54 km/h, and 40 + 54 = 94 km/h. By Newton's second law, acceleration a = F/m = 1000 N ÷ 800 kg = 1.25 m/s².
Read the full explanation →Consider the electromagnetic radiations having wavelengths 200 nm, 500 nm and 1000 nm. Which wavelength(s) of the following can make visual sensation to a human eye?
- A.200 nm and 500 nm
- B.500 nm and 1000 nm
- C.500 nm only
- D.200 nm and 1000 nm
Show answer
The human eye responds only to visible light, which lies roughly between 400 nm (violet) and 700 nm (red), and 500 nm is the only one of the three values in that range.
Read the full explanation →Bright light is found to emit from photographer's flashgun. This brightness is due to the presence of which one of the following noble gases?
- A.Argon
- B.Xenon
- C.Neon
- D.Helium
Show answer
A photographer's flash tube is filled with xenon, which gives an intense burst of white light when a high-voltage spark passes through it.
Read the full explanation →