Answer
$dim\,Col\,A=1$
Work Step by Step
Given the null space of a 7 x 6 matrix, A is 5-dimensional;
The dimension of column space is equal to its rank.
$Rank A=n-dim\,Nul A$
$n=6$ and $dim\,Nul A=5$
therefore;
$Rank A=6-5=1$
$dim\,Col\,A=Rank\,A=1$