Arrange the following in the decreasing negative electron gain enthalpy :
`B,C,N,O`

Explanation

To arrange the elements B (Boron), C (Carbon), N (Nitrogen), and O (Oxygen) in decreasing order of their negative electron gain enthalpy, we will follow these steps:

### Step 1: Understand Electron Gain Enthalpy
- Electron gain enthalpy is defined as the energy released when an electron is added to a neutral gaseous atom. The more negative the value, the more energy is released, indicating a greater tendency to gain an electron.

### Step 2: Consider Atomic Size
- The size of the atom plays a crucial role in determining electron gain enthalpy. Smaller atoms have a stronger nuclear charge relative to their size, which allows them to attract additional electrons more effectively. As we move from left to right across a period, atomic size decreases.

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