Which of the following statements about carbon cycle is not true :-

Options

A. 71% carbon is found dissolved in oceons
B. Atmosphere only contains about 1% of total global carbon
C. Annually `4 xx 10^(18) Kg` of carbon is fixed in the biosphere through photosynthesis
D. Carbon constitute 49% of dry weight of organism and is next
to water

Answer

To determine which statement about the carbon cycle is not true, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- The first statement claims that "71% carbon is found dissolved in oceans."
- This statement is correct. The oceans are indeed a significant reservoir of carbon, containing approximately 71% of the Earth's carbon.

**Hint:** Remember that oceans play a crucial role in the carbon cycle by storing a large amount of carbon.

2. **Evaluate the Second Statement:**
- The second statement states that "atmosphere has only about 1% of total global carbon."
- This statement is also true. The atmosphere contains a small fraction of the total carbon on Earth, which is roughly around 1%.

**Hint:** Consider the distribution of carbon in different reservoirs like the atmosphere, oceans, and terrestrial ecosystems.

3. **Evaluate the Third Statement:**
- The third statement mentions that "annually 4 x 10^18 kg of carbon is fixed in biosphere through photosynthesis."
- This statement is incorrect. The correct amount of carbon fixed through photosynthesis is approximately 4 x 10^13 kg, not 4 x 10^18 kg.

**Hint:** Pay attention to the magnitude of numbers in scientific notation; small differences can indicate a significant error.

4. **Evaluate the Fourth Statement:**
- The fourth statement claims that "carbon constitutes 49% of the dry weight of organisms and is next to water."
- This statement is true. Carbon is a major component of living organisms, making up about 49% of their dry weight.

**Hint:** Think about the composition of living organisms and the importance of carbon as a building block of life.

### Conclusion:
After evaluating all four statements, the incorrect statement is the third one, which inaccurately states the amount of carbon fixed in the biosphere through photosynthesis.

### Final Answer:
The statement that is not true about the carbon cycle is: "Annually 4 x 10^18 kg of carbon is fixed in biosphere through photosynthesis." The correct figure is 4 x 10^13 kg.