Which of the following would produce a buffer solution when mixed in equal volumes?

$A$ particle of mass $1 \times 10^{-26} \ kg$ and charge $1.6 \times 10^{-19} \ C$ travelling with a velocity $1.28 \times 10^6 \ ms^{-1}$ along the positive $X$-axis enters a region in which a uniform electric field $E$ and a uniform magnetic field of induction $B$ are present. If $E = -102.4 \times 10^3 \ \hat{k} \ NC^{-1}$ and $B = 8 \times 10^{-2} \ \hat{j} \ Wbm^{-2}$,the direction of motion of the particle is:

In the adjoining figure,three capacitors $C_1, C_2,$ and $C_3$ are connected to a battery. The correct condition will be (Symbols have their usual meanings):

If $f: R \rightarrow R$ is an even function having derivatives of all orders,then which of the following is an odd function?

Electrons from excited chlorophyll molecule of photosystem $II$ are accepted first by

After $280\,days$,the activity of a radioactive sample is $6000\,dps$. The activity reduces to $3000\,dps$ after another $140\,days$. The initial activity of the sample in $dps$ is