The figure shows a system of logic gates. From the study of the truth table,it can be found that to produce a high output $(1)$ at $R$,we must have

Which one of the following pairs of gases are the major cause of 'Greenhouse effect'?

$A$ certain metal is used in the preparation of antacids. This metal accidentally catches fire and cannot be extinguished using $CO_2$. Which metal is this?

Correct increasing order of spin magnetic moment (in $B.M.$) for the following complexes is:
$(I) [FeF_6]^{-3}$
$(II) [V(H_2O)_6]^{+2}$
$(III) [Fe(H_2O)_6]^{+2}$

$A$ finite ladder is constructed by connecting several sections of $2\,\mu F$ and $4\,\mu F$ capacitor combinations as shown in the figure. It is terminated by a capacitor of capacitance $C$. What value should be chosen for $C$ such that the equivalent capacitance of the ladder between the points $A$ and $B$ becomes independent of the number of sections in between? (Answer in $\mu F$)

$\int \frac{3^x dx}{\sqrt{9^x-1}}$ is equal to