The sodium ion is not an electrophile — option 1.

What an electrophile is. The word means “electron-loving”. An electrophile is a species that is electron-deficient and that attacks a region of high electron density, accepting a pair of electrons to form a new covalent bond. It is therefore a Lewis acid. The last part of that definition is what matters here.

Why a positive charge is not enough. This is the point of the question. Na⁺ carries a full positive charge and is therefore attracted to negative charge — but attraction is not the same as bonding. Having achieved the neon configuration by losing its single valence electron, sodium has no vacant low-energy orbital in which to accept a pair, and the compounds it forms are held by electrostatic attraction between ions. In solution it is a spectator ion: in a reaction such as

\(\text{NaOH}+\text{HCl}\rightarrow\text{NaCl}+\text{H}_{2}\text{O}\)

the sodium ion takes no chemical part at all. The same is true of K⁺, Mg²⁺ and Ca²⁺.

The contrast. BF₃ and H⁺ both have somewhere to put an incoming pair — an empty p orbital on boron, an empty 1s orbital on the proton — and both form covalent bonds by accepting one. Other common electrophiles are the nitronium ion NO₂⁺ in nitration, AlCl₃ in Friedel-Crafts reactions, carbocations, and the carbon of a carbonyl group.

The counterpart is the nucleophile — electron-rich, a Lewis base, which donates a pair: OH⁻, CN⁻, NH₃, water.

Hence, the answer is Na⁺.