Chemical Reactions — Set 4
Chemistry · रासायनिक अभिक्रियाएं · Questions 31–40 of 40
When Iron nails are placed in Copper Sulfate solution, the blue color fades to?
Correct Answer: B. Light green
• **Light green** = Iron displaces copper to form ferrous sulfate, which has a light green color. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Yellow; C: Red; D: Colorless
Which of the following is a balanced chemical equation for the formation of water?
Correct Answer: D. $2H_2 + O_2 \rightarrow 2H_2O$
• **$2H_2 + O_2 \rightarrow 2H_2O$** = The correct answer is '$2H_2 + O_2 \rightarrow 2H_2O$'. • **mass** — Balancing ensures that the law of conservation of mass is satisfied • 💡 Wrong-option analysis: A: $H_2 + 2O \rightarrow H_2O$; B: $H + O \rightarrow H_2O$; C: $H_2 + O_2 \rightarrow H_2O$
What type of chemical reaction is the fermentation of grapes?
Correct Answer: D. Chemical change
• **Chemical change** = Fermentation is a chemical change because sugar is converted into alcohol and carbon dioxide. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Physical change; B: Neutralization; C: Reversible change
Which gas is produced when Sodium Bicarbonate reacts with Acetic Acid?
Correct Answer: C. Carbon dioxide
• **Carbon dioxide** = The reaction between baking soda and vinegar produces brisk effervescence of carbon dioxide. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Oxygen; B: Carbon monoxide; D: Hydrogen
Copper vessels develop a green coating when exposed to moist air due to?
Correct Answer: A. Copper carbonate and hydroxide
• **Copper carbonate and hydroxide** = The green layer is a mixture of basic copper carbonate and copper hydroxide. • (Contextual detail from explanation) • 💡 Wrong-option analysis: B: Copper nitrate; C: Copper oxide; D: Copper sulfate
Which of the following is considered the most definitive indicator that a chemical reaction has occurred, as it confirms the formation of a new substance?
Correct Answer: C. Formation of a precipitate
• **Formation of a precipitate** = The formation of a precipitate (an insoluble solid formed from two solutions) is considered one of the most definitive indicators of a chemical reaction because it directly demonstrates the formation of a new substance with different solubility properties. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Change in colour; B: Evolution of gas; D: Change in temperature
What happens to the oxidation number of an element during oxidation?
Correct Answer: D. It increases
• **It increases** = Oxidation involves the loss of electrons, which leads to an increase in the oxidation state. • **Oxidation** — Oxidation involves the loss of electrons, which leads to an increase in the o... • 💡 Wrong-option analysis: A: It remains constant; B: It becomes zero; C: It decreases
Which of the following is a common reducing agent used in metallurgy?
Correct Answer: D. Carbon (Coke)
• **Carbon (Coke)** = Carbon is used to extract metals from their oxides by removing oxygen. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Oxygen; B: Chlorine; C: Water
The formula $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl$ represents which reaction?
Correct Answer: C. Double displacement
• **Double displacement** = Sodium and barium ions swap their partners to form new salt compounds. • (Contextual detail from explanation) • 💡 Wrong-option analysis: A: Displacement; B: Combination; D: Decomposition
What is the primary reason for balancing a chemical equation?
Correct Answer: A. To satisfy Law of Conservation of Mass
• **To satisfy Law of Conservation of Mass** = The correct answer is 'To satisfy Law of Conservation of Mass'. • **Mass** — The correct answer is 'To satisfy Law of Conservation of Mass' • 💡 Wrong-option analysis: B: To calculate speed; C: To show state; D: To make it look better