Biological membranes are selectively permeable, allowing certain molecules to cross the membrane, but not others. classify the molecules or ions depending on how they cross a biological membrane. note that some of these examples may also utilize active transport to traverse a membrane. however, this question is limited to passive transport processes only.

Biological membranes are selectively permeable because they permit the transport of small molecules,gases and non polar,hydrophobic compounds across themselves.

Explanation:

Water is passed through the plasma membrane by facilitated diffusion with the help of a protein known as aquaporins which act as channel proteins.

     Various ions such as Na+,K+,Ca2+ are transport across the plasma membrane through various ion channel with the additional requirement of energy in form of ATP.

Example   Na+K+ATPase,H+ATPase,Ca2+ATPase etc.

Passive transport helps in the transport of gases,water molecules along their concentration gradient that is from high concentration region to the region of low concentration until the concentration of solute molecules in both the region becomes equal.

Example Diffusion,Osmosis.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms

i would say b

explanation:

but i think i would need more information than that