Elements on the periodic table are arranged in groups because they have similar properties. these similar properties are the result
a. having the same number of neutrons in their nuclei
b. having the same number of valance electrons in their outer energy levels
c. having the same number of protons in their nuclei
d. having the same atomic masses

B. Having the same number of  valence electrons in their outer energy levels.

Explanation:

We are given that elements on the periodic table are arranged in groups because they have similar properties.

We have to fill the blank space.

Elements on the periodic table are arranged in groups because they have similar properties.

The elements have similar properties because they have same number of  electrons in their outer energy level.

Therefore, these similar properties are the result of having the same number of  valence electrons in the outer most shell.

Therefore, option B is true.

c.) polymerase chain reaction

- "unlike the original dna fingerprinting method, dna profiling does not use restriction enzymes to cut the dna. instead it uses the polymerase chain reaction (pcr)? to produce many copies of specific str sequences. pcr is an automated procedure that generates lots of copies of a specific sequence of dna."