Which of the following processes does not use a catalyst?

Passage cells are thin-walled cells found in

The variation of magnetic susceptibility $(\chi )$ with temperature for a diamagnetic substance is best represented by

Two rods of different materials having coefficients of linear expansion $\alpha_1$ and $\alpha_2$ and Young's moduli $Y_1$ and $Y_2$ respectively are fixed between two rigid massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of rods. If $\alpha_1 : \alpha_2 = 2 : 3$,the thermal stress developed in the two rods is equal provided $Y_1 : Y_2$ is equal to:

$\log _4 2 - \log _8 2 + \log _{16} 2 - \dots$ is equal to

The variance of $20$ observations is $5$. If each observation is multiplied by $2$,then the variance of the resulting observations is: