Science — CBSE Class 10 board question

Option (B): Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

The Assertion is correct. The Reason is also true — placenta is indeed a disc embedded in the uterine wall — but it merely describes the structure of the placenta, not how it provides nutrition to the embryo.

• The A is directly from the textbook: "The embryo gets nutrition from the mother's blood with the help of a special tissue called placenta."
• The R is also textbook-accurate: "This is a disc which is embedded in the uterine wall."
• However, R explains the location/structure of the placenta, not the mechanism of nutrition transfer (villi, blood spaces, large surface area). So R does not explain A — hence option (B).