Assertion : X-rays can penetrate through the flesh but not through...

Hardness penetrating power of X-ray depends upon accelerating voltage applied across $\mathrm{X}$-ray tube. Characteristic $\mathrm{X}$-ray relate to the material of target. X-ray can't pass through matter of heavier element like bones (which contain phosphorus and calcium) but can pass through matter of lighter element as flesh (which contain oxygen, hydrogen and carbon).