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

$A$ straight line makes an angle of $135^\circ$ with the $x$-axis and cuts the $y$-axis at a distance of $-5$ from the origin. The equation of the line is:

The angle between the pair of straight lines formed by joining the points of intersection of $x^2+y^2=4$ and $y=3x+c$ to the origin is a right angle. Then $c^2$ is equal to

The radioactivity of a given sample of whisky due to tritium (half-life $12.3$ years) was found to be only $3\%$ of that measured in a recently purchased bottle marked "$7$ years old". The sample must have been prepared about:

Find the correct stability order for the following carbocations:

$A$ cell is connected between the points $A$ and $C$ of a circular conductor $\text{ABCD}$ of center $O$ with angle $\angle AOC = 60^{\circ}$. If $B_1$ and $B_2$ are the magnitudes of the magnetic fields at $O$ due to the currents in arc $\text{ABC}$ and arc $\text{ADC}$ respectively,the ratio $\frac{B_1}{B_2}$ is