Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Strontium was found in a mineral from the Strontian mine (strontianite), which gave it its name. It was discovered in 1808, the same year as magnesium, calcium and barium.
Fireworks in the Edo period were made mainly from saltpeter, ash and sulfur. Around 1887, in the Meiji period, the fireworks maker Kagiya Yahei, the eleventh of that name, succeeded in making colored “Western fire” fireworks using strontium carbonate and barium sulfide.
Strontium is in the fifth row of Group 2, directly below calcium and directly above barium.
There is no single right answer. Talking it over with someone at home is a good way to learn.