What colour does the strontium ion produce in a flame test?

Strontium ions produce red colour in a flame test.

 Since each element has a precisely defined line emission spectrum The colour of the flame produced may be used by scientists to identify it.A blue flame is produced by copper, a red flame by lithium and strontium, an orange flame by calcium, a yellow flame by sodium, and a green flame by barium.

 Hence, option A is correct.