Question

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Explanation:

1. Valence Electrons: Alkali metals have 1 valence electron, while halogens have 7 valence electrons.
2. Ion Formation: Alkali metals lose 1 electron to form +1 cations; halogens gain 1 electron to form -1 anions.
3. Physical State (STP): Alkali metals are soft, shiny solids; halogens are typically diatomic gases (F₂, Cl₂), liquid (Br₂), or solid (I₂) with dull, non-metallic appearances.
4. Chemical Reactivity: Alkali metals react vigorously with water to produce alkaline metal hydroxide and hydrogen gas; halogens react with metals to form salts, and with water to form acidic solutions.

Answer:

1. Alkali metals have 1 valence electron, halogens have 7 valence electrons.
2. Alkali metals form +1 cations; halogens form -1 anions.
3. Alkali metals are soft, metallic solids at standard conditions; most halogens are non-metallic gases/liquids at standard conditions.
4. Alkali metals react with water to make alkaline solutions; halogens react with water to make acidic solutions.