From which plant did $D.J. Ivanowsky$ discover viruses?

The radius of the circle $r = 12 \cos \theta + 5 \sin \theta$ is

$A$ weight $W$ can be hung in any of the following four ways by a string of the same type. In which case is the string most likely to break?

Which one of the following statements is not correct?

$Fe$ is made passive by

Wires $A$ and $B$ are made from the same material. $A$ has twice the diameter and three times the length of $B$. If the elastic limits are not reached,when each is stretched by the same tension,the ratio of energy stored in $A$ to that in $B$ is