Answer: Option 3 - A and D
Let's break down the statements:
(A) Definition of biological species was given by Ernst Mayr:
Correct. Ernst Mayr proposed the biological species concept, which defines species as groups of interbreeding natural populations that are reproductively isolated from other such groups.
(B) Photoperiod does not affect reproduction in plants:
Incorrect. Photoperiod is a critical environmental factor that affects the reproductive behavior of many plants. Plants are classified based on their response to the length of day and night, such as long-day plants (LDP), short-day plants (SDP), and day-neutral plants. Photoperiod has a significant role in the timing of flowering and reproduction.
(C) Binomial nomenclature system was given by R.H. Whittaker:
Incorrect. Binomial nomenclature, the system of giving species a two-part Latin name (genus and species), was established by Carl Linnaeus. R.H. Whittaker contributed to the five-kingdom classification system, not binomial nomenclature.
(D) In unicellular organisms, reproduction is synonymous with growth:
Correct. In unicellular organisms, such as bacteria, reproduction (by binary fission) is often considered synonymous with growth, as the organism divides and multiplies into two identical cells, resulting in an increase in population size.
The two correct statements are (A) and (D), which makes Option 3 the correct answer.
Consider a water tank shown in the figure. It has one wall at \(x = L\) and can be taken to be very wide in the z direction. When filled with a liquid of surface tension \(S\) and density \( \rho \), the liquid surface makes angle \( \theta_0 \) (\( \theta_0 < < 1 \)) with the x-axis at \(x = L\). If \(y(x)\) is the height of the surface then the equation for \(y(x)\) is: (take \(g\) as the acceleration due to gravity) 
A constant voltage of 50 V is maintained between the points A and B of the circuit shown in the figure. The current through the branch CD of the circuit is :