Which of the Following Molecules CANNOT Freely Cross Biological Membranes

Question

Which of the following molecules CANNOT freely cross biological membranes? A) O2 B) CO2 C) NH4⁺ D) N2 E) H2

Accepted Answer

The molecule NH₄⁺ (which represents a sulfo-N-hydroxysuccinimide group) contains charged groups, making it polar and unlikely to cross biological membranes. The other options are all nonpolar and could freely cross membranes.