Why is a skin cell different from a muscle cell

Skin cell serves a completely different purpose. Muscle cells have large amount of mitochondria in them and are energy rich to perform functions that require movement. They are more durable than epithelial cells. Epithelial cells (skin cells) are quickly shed, quickly replaced, lack mitochondria and are mass produced by the body.

Why is muscle skin by skin is a type of color and muscle is a cell

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom