Correct Answer - a
Electric field due to semicircular part:
`E_(2)=(lambda_(2))/(2pi epsilon_(0)R)`
Electric field due to straight part:
`E_(1x)=E_(1y)= (lambda_(1))/(4pi epsilon_(0)R)`
For net field to be along `y`-axis:
`E_(2)=E_(1x)implies (lambda_(2))/(2pi epsilon_(0)R)=(lambda_(1))/(4pi epsilon_(0)R) rArr (lambda_(1))/(lambda_(2))=2`