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

Castor oil is obtained from which of the following plants?

If $\int \frac{7x^8+8x^7}{(1+x+x^8)^2} dx = f(x) + c$,then $f(x)$ is equal to

The force required to move a body up a rough inclined plane is double the force required to prevent the body from sliding down the plane. The coefficient of friction,when the angle of inclination of the plane is $60^{\circ}$,is

Two coins $A$ and $B$ are kept in an urn. When coin $A$ is flipped,the probability of getting a Head is $1/4$,while for coin $B$ it is $3/4$. One coin is randomly chosen from this bag and tossed twice,and it falls heads on both occasions. The probability that it is coin $A$ is:

If $\sigma_1$,$\sigma_2$,and $\sigma_3$ are the conductivities of three conductors,what will be the equivalent conductivity when they are connected in series?