Which of the following is true when Balmer gave his model for hydrogen atom?

Options

A. It was not known that hydrogen lines could be explained as different of term like `R//n^(2) with R` being a constant and `n` an integet.
B. It was not known that positive charge is concentrated in a nnucleus of small size.
C. It was not known that radiant by `h v with h` being a constant and `v` a frequency.
D. Bohr knew term like `R//n^(2)` and in the process of choosing allowed the orbits to fit them, he got'' angular momentum `= n//2 pi` as a deduction.

Explanation

To determine which statement is true regarding Balmer's model for the hydrogen atom, we will analyze each statement step by step.

### Step 1: Analyze Statement A
**Statement A:** It was not known that hydrogen lines could be explained as different terms of R/n², where R is a constant and n is an integer.

**Analysis:** This statement is false. By the time Balmer proposed his formula, it was already established that the spectral lines of hydrogen could be explained using the formula R/n², where R is the Rydberg constant and n is an integer. This concept was part of the Bohr model, which was developed after Balmer's work.

**Conclusion:** Statement A is false.

### Step 2: Analyze Statement B
**Statement B:** It was not known that positive charge is concentrated in the nucleus of small size.

**Analysis:** This statement is also false. The Rutherford scattering experiment had already demonstrated that the positive charge in an atom is concentrated in a small nucleus. This was a significant finding that preceded Balmer's work.

**Conclusion:** Statement B is false.

### Step 3: Analyze Statement C
**Statement C:** It was not known that radiation is given by E = hν, where h is a constant and ν is the frequency.

**Analysis:** This statement is incorrect as well. By the time Balmer was working, the concept of quantized energy levels and the relationship between energy and frequency (E = hν) had already been established by Planck and further developed by Einstein in his photon theory.

**Conclusion:** Statement C is false.

### Step 4: Analyze Statement D
**Statement D:** Both new terms like R/n² and the process of choosing allowed orbits led to the conclusion that angular momentum is quantized as L = n(h/2π).

**Analysis:** This statement is true. Balmer's work contributed to the understanding of quantized energy levels in hydrogen, and he introduced the idea that the angular momentum of electrons in an atom is quantized. This was a significant advancement in atomic theory, leading to the formulation of the Bohr model.

**Conclusion:** Statement D is true.

### Final Conclusion
The correct answer is **Statement D**.

---