Consider the following chemical reaction : aFe2O3 (s) + bCO(g) → cFe (s) + dCO2 In the balanced chemical equation of the above, which of the following will be the values of the coefficients a, b, c and d respectively?
- A.3, 2, 3, 1
- B.1, 3, 2, 3
- C.2, 3, 3, 1
- D.3, 3, 2, 1
Correct answer
Explanation
The correct answer is B, 1, 3, 2, 3. The balanced equation is Fe2O3 + 3CO → 2Fe + 3CO2, which has equal numbers of every atom on both sides.
Balance iron first: one Fe2O3 has two iron atoms, so 2Fe is needed on the right. Fe2O3 has three oxygen atoms to remove, and each CO molecule takes one oxygen atom to become CO2, so three CO molecules are needed, giving three CO2. Check: left side 2 Fe, 3 C and 3 + 3 = 6 O; right side 2 Fe, 3 C and 6 O. This is the main reaction in a blast furnace, where carbon monoxide reduces haematite ore to iron.
A is wrong: 3, 2, 3, 1 leaves iron and oxygen unbalanced (6 Fe on the left, 3 on the right).
C is wrong: 2, 3, 3, 1 gives 4 Fe on the left but only 3 on the right.
D is wrong: 3, 3, 2, 1 gives 6 Fe on the left and only 2 on the right.
Exam tip: in the blast furnace CO is the reducing agent: Fe2O3 + 3CO → 2Fe + 3CO2.
Practice Questions
View allConsider the following statements :
Statement-I : Giant stars live much longer than dwarf stars.
Statement-II : Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct in respect of the above statements?
- A.Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
- B.Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
- C.Statement-I is correct, but Statement-II is incorrect
- D.Statement-I is incorrect, but Statement-II is correct
Show answer
Massive giant stars burn their fuel so fast that they live much shorter lives than dwarf stars, so Statement I is false and Statement II is true.
Read the full explanation →Which one of the following is a filter feeder?
- A.Catfish
- B.Octopus
- C.Oyster
- D.Pelican
Show answer
The oyster feeds by drawing water over its gills and straining out plankton and organic particles, which is filter feeding.
Read the full explanation →With reference to radioisotope thermoelectric generators (RTGs), consider the following statements :
1. RTGs are miniature fission reactors.
2. RTGs are used for powering the onboard systems of spacecrafts.
3. RTGs can use Plutonium-238, which is a by-product of weapons development.
Which of the statements given above are correct ?
- A.1 and 2 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
Show answer
RTGs power spacecraft using heat from the natural decay of plutonium-238; they are not reactors and involve no fission. In an RTG, a radioactive isotope gives off heat as it decays on its own.
Read the full explanation →Consider the following :
1. Cashew
2. Papaya
3. Red sanders
How many of the above trees are actually native to India ?
- A.Only one
- B.Only two
- C.All three
- D.None
Show answer
Of the three, only red sanders is native to India; cashew and papaya were brought from the Americas. Red sanders (Pterocarpus santalinus) is endemic to the southern Eastern Ghats, mainly the Seshachalam and nearby hills of Andhra Pradesh.
Read the full explanation →Consider the following :
1. Butterflies
2. Fish
3. Frogs
How many of the above have poisonous species among them ?
- A.Only one
- B.Only two
- C.All three
- D.None
Show answer
Each of the three groups includes species that carry toxins in their bodies to deter predators. Butterflies: the Monarch butterfly feeds as a caterpillar on milkweed and stores its bitter cardiac glycosides, so birds that eat it fall sick; its bright orange colour is a warning.
Read the full explanation →