Choanocytes are present in

How many even numbers of $3$ different digits can be formed from the digits $1, 2, 3, 4, 5, 6, 7, 8, 9$ (repetition is not allowed)?

Five identical springs are used in the following three configurations. The time periods of vertical oscillations in configurations $(i)$,$(ii)$ and $(iii)$ are in the ratio:

Which animal group possesses a pseudocoelom?

The pressure versus temperature graph of an ideal gas for equal number of moles at different volumes is plotted as shown in the figure. Choose the correct alternative.

Two non-reactive monoatomic ideal gases have their atomic masses in the ratio $2 : 3$. The ratio of their partial pressures,when enclosed in a vessel kept at a constant temperature,is $4 : 3$. The ratio of their densities is :-