Which statement identifies a characteristic of a scientific theory?
a. it’s a subjective
b. it’s a proven fact
c. it’s based on a opinion
d. it may change over time

The correct answer is B it"s a proven fact.

Explanation:

Any scientific theory is based upon many experiments ans observations.The experiment and observations are repeated many times to provide a scientific logic about that theory.

   A scientific theory is accepted only when that theory is logically proved by various experiment ,observations,statistical analysis etc.

- 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