Which genetic disorders, caused by an extra X chromosome (XXY), is characterized by a lack of testicular development in males, effeminate features, possible mental impairment, and a thin stature?

The genetic disorder with (XXY) is Klinefelter syndrome.

The genetic disorders which is caused by an extra X chromosome (XXY) is called Klinefelter syndrome. In this disorder additional copies of genes interferes with the development of testes. This means sufferer of this disorder produces less male sex hormone (testosterone) which results into small testes. Other features may develop such as enlarged breast, thin stature and mental impairment.

D) Klinefelter's syndrome