The decay rate for a certain mass of a radioactive substance measured at different times varies with time as shown in the figure. The count rate at $t = 8 \, hr$ will be:

$A$ cylindrical metallic rod,in thermal contact with two heat reservoirs at its two ends,conducts an amount of heat $Q$ in time $t$. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. The amount of heat conducted by the new rod,when placed in thermal contact with the same two reservoirs in time $t$,is:

$A$ particle at the end of a spring executes simple harmonic motion with a period $t_1$,while the corresponding period for another spring is $t_2$. If the period of oscillation with the two springs in series is $T$,then

Match the following columns:

Column-$I$	Column-$II$
$(a)$ $Oscillatoria$	$(p)$ $Prothallus$
$(b)$ $Cycas$	$(q)$ $Cell$ $wall$ $contains$ $chitin$ $mixed$ $with$ $cellulose$
$(c)$ $Dryopteris$	$(r)$ $Primitive$ $flowers$
$(d)$ $Yeast$	$(s)$ $Food$ $stored$ $as$ $starch$

The velocities of three particles of masses $20 \ g$,$30 \ g$,and $50 \ g$ are $10 \hat{i}$,$10 \hat{j}$,and $10 \hat{k}$ respectively. The velocity of the centre of mass of the three particles is:

Which of the following is $NOT$ a characteristic of chemisorption?