Correct option is (D) 2.
In general terms for a polynomial the degree is the highest power
Now for degree to exist the given differential equation must be a polynomial in some differentials
Here differentials mean
The given differential equation is polynomial in differentials dy/dx and d2y/dx2
Degree of differential equation is defined as the highest integer power of highest order derivative in the equation
Here the highest derivative is d2y/dx2 and there is only one term of highest order derivative in the equation which is (d2y/dx2)2 whose power is 2 hence degree is 2