Neutron decay in the free space is given follows:
`._0n^1 rarr. _1H^1 +._(-e)^0 +[]`
Then, the parenthesis represents

Options

A. photon
B. graviton
C. neutrino
D. antineutrino

Explanation

To solve the question regarding neutron decay in free space, let's break it down step by step.

### Step 1: Understand the decay process
A neutron (symbol: n) decays into a proton (symbol: p) and emits an electron (symbol: e⁻). This process is known as beta decay, specifically beta negative decay.

### Step 2: Write the decay equation
The decay can be represented as:
\[ _0n^1 \rightarrow _1H^1 + _{-1}e^0 + ? \]
Here, we have:
- A neutron (n) on the left side.
- A proton (H) and an electron (e⁻) on the right side.

### Step 3: Identify the missing particle
In beta decay, in addition to the proton and electron, another particle is emitted to conserve certain physical quantities such as momentum and energy. This particle is known as an antineutrino.

### Step 4: Complete the decay equation
Thus, the complete decay equation is:
\[ _0n^1 \rightarrow _1H^1 + _{-1}e^0 + \bar{\nu} \]
where \(\bar{\nu}\) represents the antineutrino.

### Step 5: Conclusion
The parenthesis in the decay equation represents the antineutrino, which is essential for conserving energy and momentum during the decay process.

### Final Answer
The parenthesis represents an **antineutrino**.

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