Respuesta :

The first one is wrong, because the properties in a group are similar, not in a period. 

The second one is wrong. Elements do not get smaller as they move downward a group. 

The third one is correct, because the valence electrons determine a property of a element. 

Answer: thrid one
meganpierce070

The third answer would be the most accurate answer for this particular question. Elements in group 8A ARE the most reactive properties on the periodic table. Hope this helps you!

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