Which zone of the blast furnace has the highest temperature?

$A$ uniform cylinder of length $L$ and mass $M$ having cross-sectional area $A$ is suspended,with its length vertical,from a fixed point by a massless spring such that it is half-submerged in a liquid of density $\sigma$ at equilibrium position. The extension $x_0$ of the spring when it is in equilibrium is:

The process requiring absorption of energy is

Which of the following is an incorrect pair?

The molecular formula of diphenylmethane is $C_{13}H_{12}$. How many structural isomers are possible when one of the hydrogen atoms is replaced by a chlorine atom?

Eight different letters of an alphabet are given. Words of four letters from these are formed. The number of such words with at least one letter repeated is :