How to print the Nth column of a text file with AWK using argv

Suppose I have a text file with data separated by whitespace into columns. I want to write a shell script which takes as input a filename and a number N and prints out only that column. With awk I can do the following:

awk < /tmp/in '{print $2}' > /tmp/out

This code prints out the second column.

But how would one wrap that in a shell script so that a arbitrary column could be passed in argv?