The disease which causes immobility and fusion of vertebral joints is:

Explanation

Options [A] osteomalacia is a group of diseases in which bone resorption outpaces bone deposit[ it means there is more bone depletion than bone deposition].It is the softening of bones.Option [B] disc slip or herniated disc involves the rupture of annulus fibrosis followed by protrusion of the spongy nucleus pulposis.Option [C] arthritis is an inflammatory or degenerative disease that damage joints.Option [D] Spondylosis is the disease which causes immobility and fusion of joint. It is an age related condition in which the joint and cartilage lined disc are affected. So option [D] is right.