Which one is a hereditary disease/ mendelian disorder?

The correct option is D Phenylketonuria

• Cataracts are due to age-related changes in the lens of the eye that cause it to become cloudy or opaque.
  
• Leprosy, also known as Hansen's disease, is a chronic infectious disease caused by Mycobacterium leprae. The disease mainly affects the skin, the peripheral nerves, mucosal surfaces of the upper respiratory tract and the eyes
  
• Blindness can be due to Glaucoma (refers to four different eye conditions that can damage your optic nerve, which carries visual information from your eyes to your brain) or Macular degeneration( destroys the part of your eye that enables you to see details)
• Phenylketonuria is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a defect in the gene that helps create the enzyme needed to break down phenylalanine.
  

So, the correct answer is 'Phenylketonuria'.