I am taking a materials science course and require help with

I am taking a materials science course and require help with the following question:

The following pairs of elements can form soid solution alloys. Predict which ones will form substitutional and which ones interstitial alloys. Justify your answers.
(a) Copper and tin (bronze)
(b) Aluminum and silicon
(c) Iron and nitrogen
(d) Titanium and hydrogen

Solution

The pairs in options (a) and (b) will form substitutional because the atoms are similar sized. The pairs in option (c) and (d) are interstitial (carbon is intersitital in iron and nitorgen is about the same size).