The species which by definition has zero standard molar enthalpy of formation at `298K` is

Options

A. `Br_(2)(g)`
B. `CI_(2)(g)`
C. `H_(2)O(g)`
D. `CH_(4)(g)`

Explanation

To solve the question regarding the species that has a zero standard molar enthalpy of formation at 298 K, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition**: The standard molar enthalpy of formation (\( \Delta H_f^\circ \)) is defined as the change in enthalpy when one mole of a compound is formed from its elements in their standard states at 298 K and 1 atm pressure. By definition, the standard molar enthalpy of formation for any element in its standard state is zero.

2. **Identify the Options**: The options given are:
- A) \( \text{Br}_2 \) (bromine)
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