Why can not x rays pass through?

X-rays can pass through most objects, but there are some materials that they cannot penetrate, such as lead, concrete, and water. This is because these materials are more dense than air, and the x-rays are absorbed by the atoms in the material.

The density of a material is the amount of mass per unit volume. The more dense a material is, the more atoms it contains per unit volume. When x-rays pass through a material, they collide with the atoms in the material. The more atoms there are per unit volume, the more likely it is that an x-ray will collide with an atom and be absorbed.

Lead, concrete, and water are all very dense materials, and they contain a lot of atoms per unit volume. This is why they are able to absorb x-rays. In fact, lead is so dense that it is used to make radiation shielding for x-ray machines.