Question

Eriq, a chemist, is running tests with four unknown elements. He has found that they all bond the same way, so he knows that they are in the same group on the periodic table of elements. The table shows other properties that Eriq observed.

A 4-column table with 4 rows titled properties of four unknown elements. The first column titled element number has entries 1, 2, 3, 4. The second column titled melting point has entries 266 K, 172 K, 387 K, 53 K. The third column titled boiling point has entries 332 K, 239 K, 457 K, 85 K. The fourth column titled phase at room temperature has entries liquid, gas, solid, gas.

These four elements are most likely in group

15.
16.
17.

Answer 1

Group 17 (the halogens).

The temperatures and room‑temperature phases match F2, Cl2, Br2 and I2 respectively:
- Element 4 (mp 53 K, bp 85 K) → fluorine (gas)
- Element 2 (mp 172 K, bp 239 K) → chlorine (gas)
- Element 1 (mp 266 K, bp 332 K) → bromine (liquid)
- Element 3 (mp 387 K, bp 457 K) → iodine (solid)

These follow the expected trend down Group 17: increasing molar mass → stronger London dispersion forces → higher melting and boiling points.