Regarding a nucleus choose the correct options.

Options

A. (a) Density of a nucleus is directly proportional to mass number A
B. (b) Density of all the nuclei is almost constant of the order of `10^17kg//m^3`
C. (c) Nucleus radius is of the order of `10^-15m`
D. (d) Nucleus radius `prop` A

Explanation

To solve the question regarding the properties of a nucleus and determine the correctness of the given statements, we will analyze each statement one by one based on the properties of the nucleus.

### Step-by-Step Solution:

1. **Understanding Nuclear Density**:
- The density of a nucleus is defined as the mass of the nucleus divided by its volume. It is important to note that the density of a nucleus is approximately constant for different nuclei, regardless of their mass number (A).
- **Conclusion**: The statement that the density of the nucleus is directly proportional to the mass number (A) is incorrect.

2. **Evaluating Option A**:
- Option A states: "The density of nucleus is directly proportional to the mass number A."
- Since we established that nuclear density is constant and does not depend on A, this option is **incorrect**.

3. **Evaluating Option B**:
- Option B states: "Density of all nuclei is almost constant and is of the order of 10^17 kg/m^3."
- This is consistent with our understanding that the density of nuclei is indeed around 10^17 kg/m^3 and remains relatively constant across different elements.
- Therefore, this option is **correct**.

4. **Evaluating Option C**:
- Option C states: "The nuclear radius is of the order of 10^-15 meters."
- The nuclear radius is indeed on the order of 10^-15 meters (or femtometers), which is a well-known fact in nuclear physics.
- Hence, this option is also **correct**.

5. **Evaluating Option D**:
- Option D states: "Nuclear density is directly proportional to A."
- Similar to our analysis in Option A, this statement is incorrect as nuclear density does not depend on the mass number A.
- Therefore, this option is **incorrect**.

### Summary of Options:
- Option A: Incorrect
- Option B: Correct
- Option C: Correct
- Option D: Incorrect

### Final Answer:
- The correct options regarding the nucleus are **B and C**.