When is the '$DUB$' sound heard during the cardiac cycle?

Velocity and acceleration vectors of a charged particle moving perpendicular to the direction of a magnetic field at a given instant of time are $\overrightarrow{v}=2 \hat{i}+c \hat{j}$ and $\overrightarrow{a}=3 \hat{i}+4 \hat{j}$ respectively. Then the value of $c$ is

For the reaction sequence given below, the correct statement$(s)$ is$(are)$
image
$(A) \ P$ is optically active.
$(B) \ S$ gives Bayer's test.
$(C) \ Q$ gives effervescence with aq. $NaHCO _3$.
$(D) \ R$ is an alkyne.

If the harmonic mean between the roots of $(5+\sqrt{2}) x^2-b x+(8+2 \sqrt{5})=0$ is $4$,then the value of $b$ is

The oxidation potential of a hydrogen electrode at $pH = 10$ and $P_{H_2} = 1 \ atm$ will be ............ $V$.

Which option is correct to match section $A$ with section $B$?

Section $A$	Section $B$
$(i)$ Nitrosomonas	$(a)$ $\text{Nitrite} \rightarrow \text{Nitrate}$
$(ii)$ Agrobacterium	$(b)$ $\text{Nitrogen fixing bacteria}$
$(iii)$ Rhizobium	$(c)$ $\text{NO}_3^- \rightarrow \text{N}_2$
$(iv)$ Nitrobacter	$(d)$ $\text{Ammonia} \rightarrow \text{Nitrite}$
	$(e)$ $\text{Denitrifying bacteria}$