Assertion : In placental mammals the placenta is connected to the embryo by the umblical cord and has an essential role in the immunological protection of the embryo .
Reason : In mammals foetal components of the placenta derive initially from the chondroblast connected with embryonic derive initially from he chondroblast connected with embryonic blood stream either through its contact with the yolk sac.

Options

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

Answer

To analyze the assertion and reason provided in the question, let's break it down step by step.

### Step 1: Understanding the Assertion
The assertion states that in placental mammals, the placenta is connected to the embryo by the umbilical cord and plays an essential role in the immunological protection of the embryo.

- **Explanation**: The placenta is indeed connected to the embryo via the umbilical cord, which contains blood vessels (umbilical arteries and veins). The placenta facilitates the exchange of nutrients, gases, and waste between the mother and the fetus. Additionally, it provides immunological protection through the transfer of antibodies, particularly IgG, from the mother to the fetus.

### Step 2: Evaluating the Reason
The reason provided claims that in mammals, the fetal components of the placenta derive initially from chondroblasts connected with the embryonic bloodstream, either through its contact with the yolk sac.

- **Explanation**: This statement is incorrect. Chondroblasts are cells that produce cartilage, and they do not directly contribute to the formation of the placenta. The fetal components of the placenta primarily arise from the trophoblast layer of the blastocyst, not from chondroblasts. The connection to the embryonic bloodstream occurs through the development of blood vessels, but it is not related to chondroblasts.

### Step 3: Conclusion
Based on the analysis:
- The assertion is **true**.
- The reason is **false**.

Thus, the correct answer is that the assertion is true, but the reason is false.

### Final Answer
- **Assertion**: True
- **Reason**: False