Which of the following is a biodegradable polymer?

$A$ tower subtends angles $\alpha, 2 \alpha$ and $3 \alpha$ respectively at points $A, B$ and $C$,all lying on a horizontal line through the foot of the tower. Then $\frac{A B}{B C}$ is equal to:

Helium gas undergoes a cycle $ABCDA$ (consisting of two isochoric and two isobaric lines) as shown in the figure. The efficiency of this cycle is nearly ..... $\%$ (Assume the gas to be close to an ideal gas).

At a given instant,block $A$ is moving with a velocity of $5\,m/s$ upwards. What is the velocity of block $B$ at that instant?

$0.16 \ g$ of an organic compound containing sulphur produces $0.233 \ g$ of $BaSO_4$. The percentage of sulphur in the compound is:

$A$ particle is performing $U.C.M.$ along the circumference of a circle of diameter $50 \ cm$ with frequency $2 \ Hz$. The acceleration of the particle in $m/s^2$ is