The focal length of a convex lens will be maximum for:

Which one of the following animals is correctly matched with its particular named taxonomic category?

Let $S$ be the sample space of the random experiment of throwing simultaneously two unbiased dice with six faces (numbered $1$ to $6$) and let $E_k = \{(a, b) \in S : ab = k\}$ for $k \geq 1$. If $p_k = P(E_k)$ for $k \geq 1$, then which of the following is correct?

Among the following series of transition metal ions,the one where all metal ions have $3d^2$ electronic configuration is

Which one of the following pairs is mismatched?

The diagram shows a venturimeter through which water is flowing. The speed of water at $X$ is $2\,cm/s$. The speed of water at $Y$ (taking $g = 1000\,cm/s^2$) is ........ $cm/s$.