Option (1) is the correct answer because Arthritis is inflammation of joints. Option (3) is incorrect because myasthenia gravis is an immune disorder affecting neuro-muscular junction leading to fatigue, weakening and paralysis of skeletal muscle. Option (4) is incorrect because muscular dystrophy is progressive degeneration of skeletal muscle mostly due to genetic disorder. Option (2) is incorrect because tetany is rapid spasms in muscle due to low Ca++in body fluid.