Which of the following sulfates is insoluble in water?

$A$ particle moves along a circle of radius $\frac{20}{\pi} \; m$ with constant tangential acceleration. If the velocity of the particle is $80 \; m/s$ at the end of the second revolution after motion has begun,the tangential acceleration is:

Which of the following metals releases hydrogen gas upon reaction with cold dilute $HNO_3$?

Who proposed the binomial nomenclature system?

The potential difference between $A$ and $B$ in the figure is ................. $V$.

$A$ concave mirror gives an image three times as large as the object placed at a distance of $20 \ cm$ from it. For the image to be real,the focal length should be ...... $cm$.