What is common about the elements of a period? select all that apply. they have the same number of electron energy levels. they have similar chemical characteristics. they have similar physical characteristics. they transition from a metal to noble gas.

They have the same number of electron energy levels.

They transition from a metal to noble gas.

Explanation:

Periods in the periodic table of elements refer to elements in the same row. All the elements in a certain row of the periodic table;

have the same number of electron energy levels.

transition from a metal to noble gas.

a. a clone will be physically identical to the original, but won’t be genetically identical

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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.