According to the octet rule, what is true about the reactivity of halogens? a halogen atom has seven electrons in its valence shell, so halogens are very reactive. a halogen atom has two electrons in its valence shell, so halogens are very unreactive. a halogen atom has two electrons in its valence shell, so halogens are very reactive. a halogen atom has seven electrons in its valence shell, so halogens are very unreactive.

A halogen atom has seven electrons in its valence shell, so halogens are very reactive. (Option A)

Explanation: The elements in-group 7 are often referred as “halogens”.  When they form ions, they tend to gain an electron and form negative ions. They are all non-metals and their reactivity down the group decreases because the atomic radius increases in size (so fluorine is the most reactive halogen of group 7)

- 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