The section presents a question related to the periodic table of elements, specifically asking why elements in the same group exhibit similar chemical properties. The options provided for the answer include:

A. Similar number of protons  
B. Similar number of electrons in the outermost shell  
C. Similar number of neutrons  
D. All are incorrect  

The key topic is the relationship between the arrangement of elements in the periodic table and their chemical properties, with a focus on the significance of electron configuration in determining these properties.