Grignard reagent is represented as:

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Accepted Answer

Step 1: Definition

Grignard reagents are organomagnesium halides with the general formula $RMgX$, where $R$ is an alkyl or aryl group and $X$ is a halide (Cl, Br, I).

Step 2: Examine options

1) "CH -Ca-F3" — this is an organocalcium(III) fluoride notation (uses Ca), not an organomagnesium halide.

2) "CH -Be-F3" — involves Be (beryllium), not magnesium; beryllium compounds are not Grignard reagents.

3) "CH -Mg-Cl3" — interpreted as $\mathrm{CH_3\!\! - Mg - Cl}$ (methylmagnesium chloride), which fits the form $RMgX$ and is a classical Grignard reagent.

4) "H-Mg-H" — this is magnesium hydride (or a dihydride motif), not an organomagnesium halide.

Step 3: Conclusion

Only option (3) matches the Grignard general formula $RMgX$ (here $R=\mathrm{CH_3}$ and $X=\mathrm{Cl}$). FINAL_ANSWER: c

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