IGCSE Chemistry - Fundemantal Ideas

Explanation
Potassium and sodium are in the same group because they both react in a similar way. This means that they have similar chemical properties and react with other elements in similar ways. Additionally, both potassium and sodium have one electron in their outer shell, which makes them highly reactive and likely to form compounds with other elements.

Explanation
The atomic number of sodium is 11, which represents the number of protons in an atom of sodium. Therefore, there are 11 protons in an atom of sodium. The word "eleven" is simply another way of expressing the number 11.

Explanation
The atomic number of an element represents the number of protons in its nucleus. Since the atomic number of sodium is 11, it means that there are 11 protons in a sodium atom. The mass number of an atom is the sum of its protons and neutrons. In this case, the mass number of sodium is given as 23. To find the number of neutrons, we subtract the atomic number (11) from the mass number (23). Therefore, there are 12 neutrons in an atom of sodium with a mass number 23.

Explanation
This answer is correct because it accurately describes the reaction between sodium and chlorine. Two sodium atoms react with two bonded chlorine atoms, resulting in the formation of one chlorine molecule. This reaction produces two sodium ions and two chloride ions, which then combine to form two molecules of sodium chloride.