Answer : Arsenic and silicon are similar in that they both are, Metalloids.
Explanation :
As we know that there are three types of elements in a periodic table which are, metals, non-metals and metalloids.
For example : All the alkali or alkaline earth metals that is group 1 and 2 are the metals.
For example : All the p-block elements that is group 13 to 18 are the non-metals.
For example : Boron, silicon, germanium, arsenic, antimony, tellurium, polonium and astatine are the metalloids.
As per question, Arsenic and silicon are similar in properties because both are the elements of metalloids.
Hence, the arsenic and silicon are similar in that they both are, Metalloids.