Answer
It is an arithmetic sequence.
$d=5$
Work Step by Step
A sequence is arithmetic if $a_2-a_1=a_3-a_2=a_4-a_3=a_5-a_4=...=d$
For the given sequence we have that:
$a_2-a_1=9-4=5$
$a_3-a_2=14-9=5$
$a_4-a_3=19-14=5$
$a_5-a_4=24-19=5$
It is an arithmetic sequence.
Common difference: $d=5$