Molybdenum is used as a target element for the production of X – rays because it is:

light and can easily deflect electrons light and can absorb electrons a heavy element with a high melting point an element having high thermal conductivity

a heavy element with a high melting point

Molybdenum is used as a target element for production of X-rays because  In $X$-ray tube, target must be heavy element with high melting point.