Similar problem on mine - the following keys were either sticky or not functioning:
0 - = ] # ' / n b and the 'previous page' key on the top row.
I opened up the Chromebook, took out the keyboard (careful with the two ribbon connectors) and spotted that there were crumbs and dust inside. I wondered if these might have come through the keyboard, so using a compressed air can, blew air through the keyboard from all angles, giving it a really good shake and clean.
Having gently blown away any crud from the interior of the Chromebook, I reassembled the thing and found no more sticky/non-functioning keys.
Message to self: easy on the biscuits...