Which is true about each element in a period or horizontal row of the periodic table? a. each element has one more outer shell than the element before it. b. each element has one more outer electron than the element before it. c. each element has one more isotope than the element before it. d. each element bonds with the element before it.

The  true  about element in  period or  horizontal  row  of periodic table is

Each  element  has one more outer electron than the element before it. (answer B)

 Explanation

 In periodic table  there are four horizontal rows(periods) that is  period 1,2,3 and 4.

Across the period each element has one more electron than element before it.

For example  Na and Mg which  are in  periodic 3.

Na  has 2.8.1  or [Ne] 3s¹ electron configuration  while Mg has  2.8.2  or [Ne] 3S² electron configuration.

Since Mg has 2   outer electrons  while Na has 1 outer electron, Mg has more electron than Na.

a c d and f

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