Which of the following elements is a nonmetal? a. selenium (se) b. yttrium (y) c. barium (ba) d. calcium (ca) e. all of these are metals.

The correct answer option is a. Selenium (Se).

Explanation:

From the given answer options, Selenium (Se) is the only element which is a non metal.

It has the atomic number 34 with atomic weight 78.96. It is a member of the sulfur group of the non metallic elements and falls in period 4 of the Periodic table.

Selenium has non metallic properties which are intermediate between the elements that lie above and below it in the Periodic table.

a. Selenium

Explanation:

Selenium is a non metal but though rarely, it is considered to be a metalloid.

(Metalloids are elements intermediate between metals and nonmetals and are known to have partly metallic and partly non metallic properties.)

Selenium is in group 16 of the periodic table below sulphur and has average properties of the group elements above and below it in the periodic table..  

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.