Which one of the following ions is the most stable in aqueous solution? (At. No. $Ti = 22, V = 23, Cr = 24, Mn = 25$)

The value of the series $x \log _e a + \frac{x^3}{3!} (\log _e a)^3 + \frac{x^5}{5!} (\log _e a)^5 + \dots$ is

$A$ thin rod of length $L$ is bent to form a semicircle. The mass of the rod is $M$. What will be the gravitational potential at the centre of the circle?

Which one of the following molecules contains both ionic and covalent bonds?

If the pair of straight lines given by $Ax^2 + 2Hxy + By^2 = 0$ $(H^2 > AB)$ forms an equilateral triangle with the line $ax + by + c = 0$,then $(A + 3B)(3A + B)$ is equal to:

What is formed when $HCOOH$ reacts with concentrated $H_2SO_4$?