A calcium atom has {Fill in the blank} valence electrons. It needs to transfer {Fill in the blank} electrons to oxygen to have a full outer shell. An oxygen atom has {Fill in the blank} valence electrons. It needs to accept {Fill in the blank} electrons from calcium to have a full outer shell. After the transfer of electrons, calcium becomes an ion with a charge of {Fill in the blank} and oxygen becomes an ion with a charge of {Fill in the blank}.
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2 , 2, 6,2,+2,-2

Explanation:

A calcium atom has 2 valence electrons. It needs to transfer 2 electrons to oxygen to have a full outer shell. An oxygen atom has 6 valence electrons. It needs to accept 2 electrons from calcium to have a full outer shell.

After the transfer of electrons, calcium becomes an ion with a charge of +2 and oxygen becomes an ion with a charge of -2

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.