The correct option is C x−y=1
Standard from of line in two variables: ax+by=c, where x,y are variables and a,b,c are constants and the a and b cannot be zero.
⇒y=2, it can be written as 0x+y=2. But the cofficient of x cannot be zero. So, it does not represent a line in two variables.
⇒2x2−5y=1, the power of x is not unity. So, it does not represent a line.
⇒x−y=1, it has two variable x,y and coefficients are not zero. So, it represents a line in two variables.
⇒xy=5, it has two variables but the variables are multiplied together. This equation does not represent linear equations.