Question

enq, 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 enq observed.
properties of four unknown elements
element # | melting point | boiling point | phase at room temperature
1 | 266 k | 352 k | liquid
2 | 172 k | 236 k | gas
3 | 387 k | 457 k | solid
4 | 53 k | 85 k | gas
these four elements are most likely in group
15.
16.
17.
18.

Explanation:

Step1: Recall group properties

Group 17 (halogens) has elements with varying states: F₂ (gas, low mp/bp), Cl₂ (gas, higher than F₂), Br₂ (liquid), I₂ (solid).

Step2: Match with data

Element 4 (gas, low mp/bp) like F₂; Element 2 (gas, higher mp/bp) like Cl₂; Element 1 (liquid) like Br₂; Element 3 (solid) like I₂. This matches group 17. Groups 15,16,18 don't have this state variation.

Answer:

17