What is Silent in "Scent" the S or the C ? Watch
Neither; scent is pronounced that way because there are two graphemes at the start which stand for the phoneme [s]. It's as if the word were spelt "ssent" - we wouldn't say that either "s" is silent if that were the case.
The words <cent> <sent> and <scent> are homophones.
In Standard British English, the words are all pronounced /sɛnt/ (IPA)
I would argue that according to the written IPA form, the <c> is silent. If it was pronounced alongside the <s> then it would be /skɛnt/ (skent)
However, as <cent> is also /sɛnt/, we could look at how the <s> would be if it was pronounced alongside the <c>. Assuming <c> represents /s/, the two letters together would be /ssɛnt/ which would probably shorten to /sɛnt/
So surely, <c> is the silent letter. In the first instance, turning it into a sound would change the sound of the word. In the second instance, where we don't, it doesn't matter anyway.
And yes, I know this is bad logic and I am joking.