After implantation, finger-like projections appear on the trophoblast…

The correct answer is Option (3) → Chorionic villi

After the blastocyst is implanted in the endometrium, its outer layer (the trophoblast) sends out finger-like projections. These are the chorionic villi. They are surrounded by the uterine tissue and the mother’s blood. The chorionic villi and the uterine tissue fit into each other and together form the placenta, the link between the foetus and the mother’s body.

NCERT Extract:
Pregnancy and Embryonic Development – “After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta (Figure 2.12).”