A : Universe is expanding
R : There is red shift in the spectra of galaxies

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true and R is not the correct explanation of A
C. A is true and R is false
D. Both A and R are false

Answer

To solve the question regarding the assertion and reason about the universe's expansion and the redshift in the spectra of galaxies, we can follow these steps:

### Step 1: Understand the Assertion
The assertion states that "the universe is expanding." This is a well-established scientific fact supported by various observations, including the movement of galaxies away from us.

**Hint:** Recall the key evidence supporting the expansion of the universe, such as Hubble's Law.

### Step 2: Understand the Reason
The reason provided is "there is redshift in the spectra of galaxies." Redshift occurs when light from an object is stretched to longer wavelengths as the object moves away from the observer. This phenomenon is observed in the light from distant galaxies, indicating they are moving away from us.

**Hint:** Consider how the Doppler effect applies to light and how it relates to the movement of galaxies.

### Step 3: Establish the Connection
Next, we need to determine if the reason (redshift) is a correct explanation for the assertion (universe is expanding). The redshift of light from galaxies is indeed a direct consequence of the expansion of the universe. As galaxies move away, the light they emit is redshifted, indicating that the space between us and those galaxies is expanding.

**Hint:** Think about how the redshift correlates with the distance of galaxies and the rate of expansion.

### Step 4: Conclusion
Both the assertion and the reason are true, and the reason is the correct explanation for the assertion. Therefore, we conclude that both statements are true and that the reason explains the assertion.

**Final Answer:** Both assertion and reason are true, and the reason is the correct explanation of the assertion.

### Summary:
- **Assertion (A)**: True - The universe is expanding.
- **Reason (R)**: True - There is redshift in the spectra of galaxies.
- **Conclusion**: Both are true, and R is the correct explanation for A.