A new element was discovered. Using your knowledge of chemistry, explain how you would decide if the element belonged in group 1 or group 7.

Group 1 elements are metals and are known as alkali metals. They are so called because they form alkalis (basic compounds) when dissolved in water. For example, sodium (Na) is a group 1 element and forms sodium hydroxide (NaOH) when dissolved in water. Similarly, potassium (K) forms potassium hydroxide (KOH).
Group 7 elements are known as halogens and are non-metals. When dissolved in water, they form acidic solutions. For example, chlorine gas (Cl₂) when bubbled through water will form hydrogen chloride (HCl). Similarly, bromine gas (Br₂) slowly mixes with water, forming hydrogen bromide (HBr), and the resulting solution is acidic.
Thus, by making use of basic chemistry and the litmus test, we can identify if the element belongs to group 1 or group 7. Dissolve the element in water, and if it turns blue litmus to red, it belongs to group 7. On the other hand, if the resulting solution turns red litmus to blue, then the new element belongs to Group 1.
Hope this helps.