Identify the set from the following which connot form acetone in a single-step reaction.

Options

A. a.
B. b.
C. c.`(MeCOO)_(2)Ca, Me- -= -H`
D. d.

Explanation

To solve the question of which set cannot form acetone in a single-step reaction, we need to analyze each option provided. Acetone (C3H6O) is a simple ketone, and we will determine if the compounds in each option can be converted to acetone through a single-step reaction.

### Step-by-Step Solution:

1. **Understanding Acetone Formation**:
- Acetone is a three-carbon ketone. To form acetone, we need to identify reactions that can yield this compound directly from the given starting materials.

2. **Analyzing Each Option**:
- **Option A**: A secondary alcohol.
- Secondary alcohols can be oxidized to ketones using oxidizing agents (e.g., CrO3). Therefore, this option can form acetone in a single step.

- **Option B**: An alkene (specifically, methylene).
- Alkenes can undergo ozonolysis, which can break the double bond and form carbonyl compounds, including acetone. Thus, this option can also form acetone in a single step.

- **Option C**: Calcium acetate.
- When calcium acetate is heated, it can decompose to form acetone. Therefore, this option can also yield acetone in a single step.

- **Option D**: A terminal alkyne.
- Terminal alkynes can react with dilute H2SO4 in the presence of mercuric ions (Hg2+) to form an enol intermediate, which can tautomerize to yield a ketone. In this case, it can form acetone. Thus, this option can also yield acetone in a single step.

3. **Identifying the Correct Answer**:
- After analyzing all options, we find that all the options (A, B, C, and D) can form acetone in a single-step reaction. However, if we consider the possibility of an ethynyl compound (ethyne) instead of a terminal alkyne, it would not yield acetone in a single step.
- Therefore, if we assume that option D refers to a compound that cannot form acetone directly, we conclude that it is the only option that does not directly yield acetone.

### Conclusion:
- The answer to the question is **Option D**. This compound cannot form acetone in a single-step reaction.