Which of the following is false?
the endoderm, mesoderm, ectoderm are germ layers.
the trophoblast is a germ layer.
the inner cell mass is a source of embryonic stem cells.
the blastula is often a hollow ball of cells.

The trophoblast is a germ layer.

Explanation:

A trophoblast is a germ layer that refers to a cell layer that comprises the outer layer of a blastocyst, a cell cluster that will eventually turn into an embryo.

The trophoblast plays an important role in embryonic implantation and development, and the cells it contains are among the first to begin to differentiate as a fertilized egg divides to produce an embryo.  In conclusion, these cells develop in the placenta, the mother-fetus interface designed to provide a channel for nutrients and waste products.

4

a covalent bond, specfically triple bond