Which of the following are not a unit of time ?

Options

A. Second
B. Parsec
C. Year
D. Light year

Explanation

To determine which of the given options are not units of time, we will analyze each option one by one.

### Step 1: Analyze the first option - Second
- The first option is "second."
- A second is a fundamental unit of time in the International System of Units (SI).
- Therefore, **second is a unit of time**.

### Step 2: Analyze the second option
- The second option is not specified in the transcript, but we will assume it is a common unit of time for analysis.
- If it is a unit like "minute" or "hour," then it is also a unit of time.
- If it is something like "day," it is still a unit of time.
- Without the specific option, we cannot conclude definitively, but we can assume it is a unit of time.

### Step 3: Analyze the third option - Year
- The third option is "year."
- A year is defined as the time taken for the Earth to complete one orbit around the Sun, which is approximately 365.25 days.
- Therefore, **year is a unit of time**.

### Step 4: Analyze the fourth option - Light year
- The fourth option is "light year."
- A light year is defined as the distance that light travels in one year.
- It is calculated based on the speed of light (approximately \(3 \times 10^8\) meters per second) and the time in seconds in a year.
- Since a light year measures distance, **light year is not a unit of time**.

### Step 5: Analyze the fifth option - Parsec
- The fifth option is "parsec."
- A parsec is a unit of distance used in astronomy, equivalent to about 3.26 light years.
- Therefore, **parsec is not a unit of time**.

### Conclusion
From the analysis:
- The first option (second) is a unit of time.
- The second option (assumed to be a common time unit) is likely a unit of time.
- The third option (year) is a unit of time.
- The fourth option (light year) is **not a unit of time**.
- The fifth option (parsec) is **not a unit of time**.

Thus, the options that are **not units of time** are **light year and parsec**.