Railway Science (Chemistry-Chemical Reaction) (Part-VII)

Total Questions: 19

1. What is that reaction called in which two compounds exchange ions and form new compounds ? [RRB Group D 23/10/2018 (Afternoon)]

Correct Answer: (d) double displacement reaction
Solution:

Combination: This reaction involves two or more elements or compounds combining to form a single new compound. Isomerization reaction: This reaction involves a rearrangement of atoms within a molecule, resulting in different isomers of the same compound.

2. Which of the following statements is/are true ? [RRB Group D 23/10/2018 (Evening)]

A. A balanced chemical equation has an equal number of atoms of all elements in the reactants and products.
B. An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products.

Correct Answer: (b) A and B are both true
Solution:

Examples - Balanced equation for photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ . , Unbalanced equation: H₂(g) + O₂ (g) → H₂O (l).

3. Fats and oils become rancid because of : [RRB Group D 25/10/2018 (Morning)]

Correct Answer: (c) oxidation
Solution:

Fats and oils oxidize or hydrolyze when they are exposed to light and air, which makes them rancid. When fats and oils in food oxidize, the meal's flavor and aroma are changed. Rancidity results in an unusual smell and taste.

4. In _______, both oxidation and reduction occur. [RRB Group D 26/10/2018 (Afternoon)]

Correct Answer: (c) redox reaction
Solution:

A combination reaction may be denoted in the manner: A + B → C. Either A and B or both A and B must be in the elemental form for such a reaction to be a redox reaction.
In a displacement reaction, an ion (or an atom) in a compound is replaced by an ion (or an atom) of another element. Decomposition reaction leads to the breakdown of a compound into two or more components, at least one of which must be in the elemental state.

5. Which of the following statements is/are true/false? [RRB Group D 26/10/2018 (Evening)]

A. The following is an example of an irreversible reaction: N₂(g)+3H₂(g) ⇌ 2NH₃(g)
B. The following is an example of a combination reaction: 2Mg(s)+O₂(g) → 2MgO(s)

Correct Answer: (d) Only B is true
Solution:

A reaction is said to be reversible if under certain conditions of temperature and pressure, the forward and reverse reactions occur simultaneously. Reversible reactions are indicated by placing two half arrows pointing in opposite directions (⇌) between the reactants and products. Example: A+ B ⇌ C+ D. Reactions that occurs only in one direction are called irreversible reactions. Example: C (s) + O₂ (g) CO₂ → (g).

6. The general reaction between a metal oxide and an acid can be written as: [RRB Group D 29/10/2018 (Morning)]

Correct Answer: (a) Metal oxide + acid ⟶ salt + water
Solution:

Metal oxide + acid→ salt + water : Example : CaO + 2HCl → CaCl₂ + H₂O. Calcium oxide (CaO) is a metallic oxide which is basic in nature. When an acid (hydrochloric acid, HCl) reacts with calcium oxide, a neutralization reaction takes place and calcium chloride (CaCl₂) along with water (H₂O) is formed.

7. Which of the following statements is/are true ? [RRB Group D 29/10/2018 (Evening)]

A. An unbalanced chemical equation has an equal number of atoms of different elements in the reactants and products.
B. A balanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products

Correct Answer: (c) A and B are both false
Solution:

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. Example - 3Fe + 4H₂O → Fe₃O₄ + 4H₂ . An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. Example - H₂ + O₂→ 2H₂O

8. This is an element belonging to the 16th group of the periodic table, which is used in the manufacture of vulcanized rubber. This element reacts with hot and concentrated HNO₃ to form sulfuric acid. Which element is this ? [RRB Group D 1/11/2018 (Evening)]

Correct Answer: (d) Sulphur
Solution:

It is added to rubber during vulcanization, a process that improves its strength and elasticity. Reaction:- S (s) + 6HNO₃ (aq)→ H₂SO₄ (aq) + 2NO₂ (g) + 3H₂O (I).

9. Which of the following metals can easily react with water? [RRB Group D 12/11/2018 (Morning)]

Correct Answer: (d) potassium
Solution:

Potassium (K), Sodium (Na), and Calcium (Ca) are the metal which reacts readily with cold water. Metals such as lead, copper, silver and gold do not react with water at all. Reactivity of metals decreases in the order: Potassium(K), Sodium (Na), Calcium (Ca), Magnesium (Mg).

10. Which of the following statements is/are true/false? [RRB Group D 12/11/2018 (Evening)]

A. The following reaction is an example of a reversible reaction:
N2(g) + 3H₂(g) ⇄ 2NH₃(g)
B. The following reaction is an example of a thermal decomposition reaction:

 

Correct Answer: (c) Both A and B are true
Solution:

Reversible reactions take place in the same reaction vessel and can proceed in the forward and backward direction simultaneously under the same conditions of temperature and pressure.
Example: A + B ⇄ C + D. Thermal decomposition reaction - When a decomposition reaction is carried out by heating.