`Delta x= (mu-1)t`, , For `mu=1, Delta x=0`
`:. I = "maximum" = I_(0)` , As `mu` increases path difference `Deltax` also increases. , or `Delta x = 0 to (lambda)/(2)`, intensity will decrease from `I_(0)` to zero. Then for `Delta x= (lambda)/(2) " to " lambda`, intensity will increase from zero to `I_(0)`. Hence option 3 is correct.