Select the correct answer. when phillip analyzed an unknown substance x, he found that it contained only one kind of atom. phillip was unable to convert the substance to a simpler one. what is substance x? a. a compound b. an element c. a heterogeneous mixture d. a homogeneous mixture

The correct answer is option B, that is, an element.  

A compound comprises of either more than one kind of atom or various similar atoms. They can be dissociated or can be converted into a simpler one. An element refers to a substance that comprises only one kind of atom. It cannot be dissociated further or can be converted into simpler substance by any chemical means.  

Heterogeneous mixture refers to a non-uniform mixture of distinct atoms without any chemical bonding in between them. On the other hand, homogenous mixture refers to a uniform mixture of distinct atoms with the absence of any kind of chemical bonding in between them.