The correct option is B −311
We know, as per associative property of rational numbers for addition we can write,
(a+b)+c=a+(b+c) [For any rational number a,b and c]
So, we can write given expression 19−5+[−311+−78] as [19−5+−311]+−78
And after comparing we can say value for the blank will be −311
Hence, option 'b' is correct.