General Chemistry

Gibbs free energy determines the spontaneity of chemical reactions under constant pressure and temperature.
Step 1: Interpret ΔG.
- If , the reaction is at equilibrium; forward and backward rates are equal. - If , the reaction is spontaneous in the forward direction. - If , the forward reaction is non-spontaneous.
Step 2: Evaluate given statements.
(A) Incorrect — does \textit{not} imply one-direction movement; it implies no net reaction.
(B) Correct — equilibrium condition.
(C) Correct — negative ΔG means spontaneous forward reaction.
(D) Correct — positive ΔG means the reaction will not proceed forward spontaneously.
Thus, the correct statements are (B), (C), and (D).
Final Answer: (B), (C), (D)

Step 1: Evaluate option (A).
Photophosphorylation = formation of ATP using light energy in chloroplasts. Correct.
Step 2: Evaluate option (B).
Phosphorylation = addition of phosphate to ADP to form ATP. This occurs in both mitochondria (oxidative phosphorylation) and chloroplasts (photophosphorylation). Correct.
Step 3: Evaluate option (C).
The Calvin cycle (C3 pathway) is universal in photosynthetic organisms, including C3 and C4 plants. Correct.
Step 4: Evaluate option (D).
This statement incorrectly assigns C4 characteristics to C3 plants. - C4 plants (e.g., maize, sugarcane) show special leaf anatomy (Kranz anatomy), tolerate high temperatures, show reduced photorespiration. - C3 plants (e.g., wheat, rice) lack these features. Thus, (D) is NOT correct. Final Answer:

Step 1: Recall definition of endogenous metabolism.
- Endogenous metabolism occurs when external substrate is absent. - Cells use their own stored material as an energy source. - In aerobic bacteria, the electron acceptor is dissolved oxygen from the environment, not inside the cells. Thus, statement (i) is incorrect, statement (ii) is correct.
Step 2: Check link with fermentation.
Fermentative metabolism occurs in the absence of oxygen. But endogenous metabolism in aerobic bacteria is linked to aerobic respiration using oxygen, not fermentation. So, statement (iii) is incorrect.
Step 3: Evaluate exogenous metabolism.
- Exogenous metabolism = when bacteria utilize external substrate (e.g., glucose). - The energy extraction involves enzyme-mediated electron transfer within the cells. So, statement (iv) is correct.
Step 4: Match with options.
- (ii) is correct. - (iii) is incorrect. Hence the correct choice is (B). Final Answer:

Step 1: Evaluate Statement I.
"Bacteriophage is an anaerobic bacterium." This is false. A bacteriophage is a virus that infects bacteria, not a bacterium itself.
Step 2: Evaluate Statement II.
"Male-specific bacteriophage infect via the pili of other microorganisms including viruses." Correction: Male-specific bacteriophages (e.g., F-phages) infect bacteria by attaching to the sex pili of bacteria (not viruses). So the spirit of this statement is partially correct if interpreted as bacterial pili, but "including viruses" is misleading. However, exam convention often accepts the role of pili.
Step 3: Evaluate Statement III.
"Bacteriophage is found in human as well as in animal excreta." This is true. Bacteriophages are commonly found in environments with high bacterial content, including sewage, soil, and animal/human feces.
Step 4: Evaluate Statement IV.
"Bacteriophage cannot indicate the presence of bacteria." This is false. Bacteriophages are viruses that require bacteria for replication. Their presence indirectly indicates bacterial hosts.
Step 5: Conclusion.
- I → incorrect - II → mostly correct (with minor misleading phrase) - III → correct - IV → incorrect Thus, the correct answer is that both (III) and (IV) are incorrect, i.e., option (C). Final Answer:

Step 1: Recall GWP values (100-year horizon).
- CH ≈ 28–30 times CO
- N O ≈ 265–300 times CO
- CFCl (CFC-11) ≈ 4660 times CO
- CF Cl (CFC-12) ≈ 10,200 times CO

Step 2: Arrange in ascending order.
CH (≈30) < N O (≈265) < CFCl (≈4660) < CF Cl (≈10,200).
Step 3: Match with options.
This corresponds to Option (C). Final Answer:

Step 1: Understanding the behavior of HgCl2 at pH 10.
At pH 10, mercury in the form of HgCl2 may undergo different processes. The student’s measurement technique detects only the free mercury ion , but other forms of mercury might be present, which are not detectable by the student’s instrument.

Step 2: Analyzing Explanations.
Explanation 1: The possibility of mercury changing phase from aqueous to gaseous is unlikely at standard conditions, as mercury vapor would need higher temperatures or specific conditions to volatilize. Hence, Explanation 1 is less likely to explain the discrepancy.
Explanation 2: Mercury at pH 10 can form various aqueous complexes, such as or , which would reduce the concentration of free mercury . This is a valid reason why the student observed a lower concentration.
Explanation 3: Mercury could have precipitated as mercury(II) hydroxide, , especially at higher pH values, further reducing the free mercury concentration.

Thus, Explanations 2 and 3 correctly explain why the student observed a lower concentration of free mercury.