Caulk normally used would not work because it s too large a gap.
Filling gap between countertop and wall.
Close the gap between counter and wall if the gap between the countertop and backsplash is more than 3 8 inch it s generally too wide to fill and is best handled with trim but you can try to close the gap to give yourself the caulk option.
I probably will be using the peel and stick kind because i have no experience with real tile.
It looks like the was was cut incorrectly and not flush.
If there is say an inch to inch and one half overhang across the front of your slab maybe the slab could be slid back say one half inch closer to the wall closing the gap enough that when you add a backsplash you could fill in the difference with foam backer stuffed into the space between back of countertop and wall and then use flexible caulk to close the gap would depend on how thick your backsplash is as to whether this might be a viable fix.
The problem is that the walls seem to have a serious bow to them and where the countertop pieces join in the corner there is about a 1 inch gap between the backsplash and the wall.
An obvious gap between a countertop and backsplash is unattractive and it can allow water to seep through.
If it s not too wide i d line the back of the counter with crown molding or wall trim of some kind paint it with a high gloss paint so that it s washable.
Once the gap cover is the right size simply slide it into the gap between the stove and the counter.
Darciegage2 has the best solution.
First get pvc tubing that s inch thicker than the gap.
You ll need a drill with a no.
Grout is no used between countertop and wall tile.
Even if the gap is small and not particularly noticeable filling the gap with caulk prevents crumbs splattered oil and other small kitchen debris from collecting behind the countertop and gives the area a more streamlined appearance.
2 phillips bit a flat pry bar wood shims and a hammer.
Slot it into the space until it s level.
Then use a pair of scissors to cut off the excess tubing.
For more information about filling the gap between the stove and the counter like how to make a guard with t molding read on.
You can also try filling the gap using plastic tubing.
As i ve evaluated my kitchen i noticed there is a large gap between my wall and countertop see photos.
The counters are flush up against the wall at the furthest ends from the corner.
If the gap is too wide to seal with silicone narrow trim molding can solve the problem.