In the reaction,$2SO_2 + O_2 \xrightarrow[As_2O_3]{Pt} 2SO_3$,$As_2O_3$ acts as:

$A$ lift is moving downwards with an acceleration equal to the acceleration due to gravity. $A$ body of mass $M$ kept on the floor of the lift is pulled horizontally. If the coefficient of friction is $\mu$,then the frictional resistance offered by the body is:

The formula of sodium nitroprusside is .........

The extent of charge of a lead accumulator is determined by

In an astronomical telescope in normal adjustment,a straight black line of length $L$ is drawn on the objective lens. The eyepiece forms a real image of this line. The length of this image is $l$. The magnification of the telescope is

Four successive members of the first series of the transition metals are listed below. For which one of them the standard electrode potential $(E^o_{M^{2+}/M})$ value has a positive sign?