It must have a medium. It must travel in empty space. Mechanical waves are waves which needs medium of propogation.
Area is 2-dimensional which means it has a length and a width area is measured in square units such as square inches, square feet or square meters. To find the area of a rectangle multiply the length by the width.
Well, electrons can be converted into a atomic number so if SE atomic number is 34 that means it has 34 electrons. AI has a atomic number of 13 meaning it has 13 electrons.
So the difference is that SE has more electrons then AI.
Hope this helped. :D
