Video Transcript
What are the three allotropic forms of arsenic? (A) Blue, black, and red; (B) violet, red, and gray; (C) yellow, black, and gray; (D) red, black, and gray; (E) red, black, and violet.
Before we begin to answer this question, let us first review allotropes, which are different structural formulas of the same element but with a different physical state. Now that we have reviewed an allotrope, this would be a good time for us to remember that this question is testing our ability to recall facts about allotropes for group 15 elements.
For this question, the physical state we are investigating are the different colors. When reviewing the allotropes involved with the group 15 elements, nitrogen and bismuth do not have any allotropic forms. We also need to remember that phosphorus, antimony, and arsenic all have black allotropes. Since arsenic is black, we can eliminate option (B) violet, red, and gray since the color option of black is not present.
When referring back to group 15 elements, phosphorus is the only element in that group that has a red and violet allotrope. Therefore, we can eliminate option choice (A) blue, black, and red; option choice (D) red, black, and gray; and option choice (E) red, black, and violet.
Now let us remember that antimony and arsenic can both have yellow allotropes. And arsenic’s most common color is a metallic-gray color. Therefore, option (C) yellow, black, and gray is the correct answer choice for what are the three allotropic forms of arsenic.
