Answer: Caesium (Cs).
- A Caesium (Cs)
- B Sodium (Na)
- C Potassium (K)
- D Lithium (Li)
Correct answer: A. Caesium (Cs)
Explanation: Caesium is the most reactive naturally occurring alkali metal, though francium is more reactive (but radioactive).
The complete modern periodic table (118 elements). Image: Cepheus et al., Public Domain, via Wikimedia Commons.
Concept context
The periodic table organises all 118 elements by atomic number and similar properties. Study periodic trends like atomic radius, ionization energy, and electronegativity, and learn how an element's position predicts its behaviour.
Read the full Classification of Elements and Periodicity in Properties notes →