There are six different ways you can spell the /k/ sound:
sky
cat
tobacco
back
question
chaos
Notice that the “ch” words come from Greek!
Can you think of other words with the sound /k/ spelled differently?
BIBLIOGRAPHY:
Evans, J.R. (1985). Spelling Made Easy. London: Macmillan
Wijk, A. (1966). Rules of Pronunciation for the English Language. Oxford: OUP
Englsh spelling rules
Spelling quiz /k/ sound
Spelling the final k Sound [exercise]