Protons and electrons are 12. For neutrons, there are 12 of them. <span>Magnesium has an </span>atomic number<span> of 12, which means there are 12 protons. You subtract the atomic number from the mass number in order to find neutrons. </span>Atomic mass is 24. 24-12=12 Electrons always match the number of protons.
There are 19 protons in the element K, you can tell because of the number 19 above the elements abbreviation. There are also 19 electrons in this element, you can tell because the number of protons is the same number of electrons. Last, to find the number of neutrons an atom possesses, you have to round the atomic mass ( 39.089 to 39 ). Then you take your Mass number ( 39 ) and subtract it from your number of protons (19). 39 - 19 = 29, there are 29 neutrons in the element K.
Hope that this helps! :)
Also if you need part 1 :)
Part 1:
The two-element that has the same properties as Magnesium are Calcium (Ca) and Strontium (Sr). These three elements are all Alkaline earth metals, they are not as reactive as Alkali metals but they are too reactive to be found in nature.
