... the Ionic Radius of Strontium.
[b] Explain your reasoning.

Answer [a] 112 pm ?? -------- based on what is this calculated or predicted??
[b] A Strontium atom [2,8,18,8,2] with 5 occupied electron shells loses 2 electrons to form a Strontium ion [2,8,18,8] with 4 occupied shells