Right after the Final Selection, the contestants were asked to pick an ore for their katanas. During Tanjiro's turn, it was depicted that he used his sense of smell to make a beneficial selection. Was this ever elaborated upon? For instance, was it ever mentioned in the anime as to what effect this had on his katana?
It is mentioned in the "Kimetsu No Yaiba Manga : Chapter 6" that :
He utilizes the Water Breathing: Fourth Form - Striking Tide to slice the 'threads' that he smelled, and successfully defeats the demons .
Though it's not mentioned anywhere, what I assume is by the time he completed final selection , he had defeated many demons as well as cut the rock with the help of his smell and breathing technique. So , even when he was asked to choose the ore , he chose to use the sense of smell as he didn't have any other parameter or knowledge to do so . So he chose smelling similar to his past actions.