Which of the following balanced chemical equations correctly represents photosynthesis in green plants?

Introduction / Context:
Photosynthesis is one of the most important biological and chemical processes on Earth. It describes how green plants, algae and some bacteria convert carbon dioxide and water into glucose and oxygen using light energy. Knowing the balanced chemical equation for photosynthesis helps students connect biological concepts with stoichiometry and chemical reactions. This question asks which equation correctly represents the overall process.

Given Data / Assumptions:
- The process is photosynthesis in green plants.
- Reactants include carbon dioxide and water, with light as the energy source.
- Products include glucose (C6H12O6) and oxygen gas (O2).
- Equations must be balanced with equal numbers of each type of atom on both sides.

Concept / Approach:
The standard overall equation for photosynthesis is written as six molecules of carbon dioxide plus six molecules of water giving one molecule of glucose and six molecules of oxygen, with light energy indicated above the arrow. Symbolically this is 6CO2 + 6H2O giving C6H12O6 + 6O2. To answer the question, we match this known equation with the options and also check that it is balanced in terms of carbon, hydrogen and oxygen atoms on both sides.

Step-by-Step Solution:
Step 1: Recall the overall photosynthesis equation: 6CO2 + 6H2O giving C6H12O6 + 6O2. Step 2: Count atoms on the left. Carbon: 6 from CO2. Hydrogen: 12 from 6H2O. Oxygen: 12 from 6CO2 plus 6 from 6H2O for a total of 18. Step 3: Count atoms on the right. Carbon: 6 in C6H12O6. Hydrogen: 12 in C6H12O6. Oxygen: 6 in C6H12O6 plus 12 in 6O2 for a total of 18. Step 4: Confirm that atom counts match, so the equation is balanced. Step 5: Compare this balanced equation with the options and see that option A exactly matches the standard form.

Verification / Alternative check:
An alternative check is to recognise the reverse relationship between photosynthesis and respiration. In cellular respiration, glucose and oxygen are converted back to carbon dioxide and water. The typical equation for respiration is C6H12O6 plus 6O2 giving 6CO2 plus 6H2O. Option B resembles this respiration equation rather than photosynthesis, which confirms that option A, written in the opposite direction with carbon dioxide and water as reactants, corresponds to photosynthesis. This relationship reinforces the correct choice.

Why Other Options Are Wrong:
Option B, C6H12O6 + 6O2 -----> CO2 + 6H2O, represents respiration rather than photosynthesis and is in the reverse direction. Option C, CO2 + H2O -----> C6H12O6 + 6O2, is unbalanced because it has only one CO2 and one H2O on the left but six carbons and twelve hydrogens on the right. Option D, 6O2 + 6H2O -----> C6H12O6 + 6CO2, incorrectly swaps the roles of carbon dioxide and oxygen and does not match the known process. These equations either describe different processes or are not properly balanced.

Common Pitfalls:
Students may confuse photosynthesis with respiration because the equations are reverses of each other. Another common error is to forget the 6 in front of CO2 and H2O in the photosynthesis equation, leading to an unbalanced equation. Some learners also think that the presence of light on the arrow changes the stoichiometry, when it actually represents energy input and not additional atoms. Keeping clear that photosynthesis builds glucose from carbon dioxide and water, while respiration breaks it down, helps prevent these mistakes.

Final Answer:
The balanced chemical equation that correctly represents photosynthesis in green plants is 6CO2 + 6H2O -----> C6H12O6 + 6O2.