To understand why the correct answer is option 'C' (23/10), let's break down the given information and go through the process step by step.

Given:
- A positron is emitted from 2311Na.

We need to find the ratio of the atomic mass and atomic number of the resulting nuclide.

Let's analyze the given information and understand the process involved.

1. Positron Emission:
- A positron is a positively charged particle, which is essentially a positively charged electron.
- Positron emission is a type of radioactive decay in which a proton in the nucleus is converted into a neutron, and a positron is emitted.
- This process decreases the atomic number by one while keeping the atomic mass constant.

2. 2311Na:
- The notation 2311Na represents the nuclide sodium-23, where the superscript 23 denotes the atomic mass and the subscript 11 denotes the atomic number.
- Sodium-23 has an atomic mass of 23 and an atomic number of 11.

Now, let's go through the process:

1. Positron emission from sodium-23:
- In this process, a proton in the nucleus of sodium-23 is converted into a neutron.
- As a result, the atomic number decreases by one, becoming 10.
- However, the atomic mass remains the same at 23.

2. Resulting nuclide:
- After the positron emission, the resulting nuclide will be identified by the new atomic number and atomic mass.
- The atomic number will be 10, and the atomic mass will remain 23.

Now, let's calculate the ratio of the atomic mass and atomic number of the resulting nuclide:

Ratio = Atomic mass / Atomic number = 23 / 10

Therefore, the correct answer is option 'C' (23/10).