Vertebral column is derived from

$A$ centigrade and a Fahrenheit thermometer are dipped in boiling water. The temperature is lowered until the Fahrenheit thermometer registers $140^{\circ}F$. What is the fall in temperature in $^{\circ}C$ as registered by the centigrade thermometer?

Which of the following will not show geometrical isomerism?

Which of the following statements is incorrect for $Nostoc$ and $Anabaena$?

The radius of the first orbit of hydrogen is $r_{H}$,and the energy in the ground state is $-13.6 \text{ eV}$. Considering a $\mu^{-}$-particle with a mass $207 m_e$ revolving around a proton as in a hydrogen atom,the energy and radius of the proton and $\mu^{-}$-combination respectively in the first orbit are (assume the nucleus to be stationary):

Two identical balls $A$ and $B$ are released from the positions shown in the figure. They collide elastically on the horizontal portion $MN$. The ratio of the heights attained by $A$ and $B$ after the collision will be: (neglect friction)