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.

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.