Which is the word in English that has nine letters and
remains a word at each step
even when you remove one
letter from it, right up to a
single letter remaining. List
each letter as you remove
them, along with the resulting
word at each step.

startling

Step by step:

remove the l, and the word becomes: starting

remove one t, and the word becomes: staring

remove the a, and the word becomes: string

remove the r, and the word becomes: sting

remove the other t, and the word becomes: sing

remove the g, and the word becomes: sin

remove the s, and the word becomes: in

remove the n, and the word becomes: I