Will give brainliest if correct.

-1

Explanation:
The slope is equal to the rise/run of the line, or in other words, the number of units the line travels upwards per the number of times the line travels to the right.

We can see that for every -1 units the line travels upwards, the line travels right 1 unit. Therefore, the slope is -1/1, which is the same as -1.

I hope this helps!

2.) is the most sense