Which of the following elements is a non-metal located in group 6A or 7A of the periodic table with atomic number less than 40?

• A. Se (selenium)
• B. O (oxygen)
• C. I (iodine)
• D. Br (bromine)

Answer: (B)

Verified step by step guidance

1. Identify the groups 6A and 7A on the periodic table. Group 6A is the chalcogens, and group 7A is the halogens.
2. List the elements given in the problem and determine their group and atomic number: Se (selenium), O (oxygen), I (iodine), Br (bromine).
3. Check which of these elements are non-metals. Non-metals in groups 6A and 7A include oxygen, sulfur, selenium, tellurium (group 6A), and fluorine, chlorine, bromine, iodine, astatine (group 7A).
4. Compare the atomic numbers of these elements to see which have atomic numbers less than 40. Oxygen (8), selenium (34), bromine (35), iodine (53).
5. Select the element that is a non-metal, belongs to group 6A or 7A, and has an atomic number less than 40. This will be the correct answer.