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The actinide series is a group of 15 chemical elements in the periodic table, spanning from Actinium (Ac, atomic number 89) to Lawrencium (Lr, atomic number 103). These elements are placed in the f-block because their valence electrons progressively occupy the 5f orbitals.
Actinides are characterized by similar chemical and physical properties. They are all metals, and most are radioactive. The first element, Actinium (Ac), marks the beginning of the actinide series, while Lawrencium (Lr) is generally considered its last member.
Key features of actinides include:
Radioactivity: Almost all actinides are radioactive, with no stable isotopes.
Oxidation states: They show a wide range of oxidation states, though +3 is the most common.
Position in the periodic table: They belong to the second row of the f-block, following the lanthanides.
Electron configuration: Progressive filling of the 5f orbital.
Nuclear applications: Some actinides, such as Uranium (U, atomic number 92) and Plutonium (Pu, atomic number 94), are widely used as nuclear fuel in reactors and in atomic weapons.
Occurrence: Only a few, like Thorium and Uranium, occur naturally in significant amounts. Most others are synthesized artificially in laboratories.
Examples of actinides with their atomic numbers:
Actinium (Ac, 89)
Thorium (Th, 90)
Protactinium (Pa, 91)
Uranium (U, 92)
Neptunium (Np, 93)
Plutonium (Pu, 94)
Americium (Am, 95)
Curium (Cm, 96)
Berkelium (Bk, 97)
Californium (Cf, 98)
Einsteinium (Es, 99)
Fermium (Fm, 100)
Mendelevium (Md, 101)
Nobelium (No, 102)
Lawrencium (Lr, 103)
In conclusion, actinides are elements with atomic numbers from 89 to 103. This makes Option 3 the correct answer.
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