Resolved questions
what are difference between 沉默& 无声 please? both of them meaning "silence"

无声 means silence, describing the physical state of someone, something or a situation.
沉默 is used for describing the mental state someone is in, either because he/she is thinking or he/she is not willing to talk or to provide information required.

someone who is 沉默的 must be 无声的, however someone who is 无声的, is not necessarily 沉默的。