Which of the following statement (s) is/are true?
I. When two or more compounds have similar molecular formula but different carbon skeletons are referred to as chain isomerism.
II. When two or more compounds differ in the position of substituent atom of functional group on the carbon skeleton, they are called non- positional isomers.
Choose correct option.

Options

A. Only I
B. Only II
C. Both I and II
D. None of the above

Answer

To determine which of the given statements is true, we need to analyze each statement carefully.

### Step-by-Step Solution:

1. **Analyze Statement I:**
- Statement I claims that when two or more compounds have similar molecular formulas but different carbon skeletons, they are referred to as chain isomers.
- **Explanation:** This is indeed correct. Chain isomerism occurs when compounds have the same molecular formula but differ in the arrangement of the carbon skeleton (i.e., the way carbon atoms are connected). For example, butane (C4H10) can exist as n-butane (a straight chain) and isobutane (a branched chain).
- **Conclusion for Statement I:** True.

2. **Analyze Statement II:**
- Statement II claims that when two or more compounds differ in the position of the substituent atom or functional group on the carbon skeleton, they are referred to as non-positional isomers.
- **Explanation:** This statement is incorrect. When compounds differ in the position of a functional group or substituent on the same carbon skeleton, they are referred to as positional isomers (or position isomerism). For example, if a hydroxyl group (–OH) is attached to different carbon atoms in a chain, these compounds are positional isomers.
- **Conclusion for Statement II:** False.

3. **Final Conclusion:**
- Since Statement I is true and Statement II is false, the correct option is that only Statement I is true.

### Answer:
The correct option is that only Statement I is true.