Which of the following is least likely to behave as a Lewis base?

The solution of $\tan y \frac{dy}{dx} = \sin(x+y) + \sin(x-y)$ is

Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?

Which of the following animals possesses a four-chambered heart?

Consider the statements given below regarding contraception and answer as directed thereafter:
$(1)$ Medical Termination of Pregnancy $(MTP)$ during the first trimester is generally safe.
$(2)$ Generally,chances of conception are nil until the mother breast-feeds the infant up to two years.
$(3)$ Intrauterine devices like Copper-$T$ are effective contraceptives.
$(4)$ Contraception pills may be taken up to one week after coitus to prevent conception.
Which two of the above statements are correct?

What are the products formed when phenyl ethyl ether is heated with concentrated $HBr$?