Which of the following statements is wrong for viroids?

What are the products formed when ammonia reacts with excess chlorine?

The bob of a simple pendulum is hanging vertically down from a fixed identical bob by means of a string of length $l$. If both bobs are charged with a charge $q$ each,what is the time period of the pendulum? (Ignore the radii of the bobs.)

Two adjacent sides of a parallelogram $ABCD$ are given by $\overline{AB}=2 \hat{i}+10 \hat{j}+11 \hat{k}$ and $\overline{AD}=-\hat{i}+2 \hat{j}+2 \hat{k}$. The side $AD$ is rotated by an angle $\alpha$ in the plane of the parallelogram so that $AD$ becomes $AD^{\prime}$. If $AD^{\prime}$ makes a right angle with the side $AB$,then the cosine of the angle $\alpha$ is given by

The venous system of a frog differs from that of a mammal due to the presence of:

Which one of the following elements,when present as an impurity in silicon,makes it a $p$-type semiconductor?