Which of the following metal undergo spontaneous combustion?

The correct option is D

lithium

• Spontaneous combustion is the phenomenon in which a hydrocarbon (or a chemical substance) substance unexpectedly bursts into flame without apparent cause.
• In this process, the substance gets oxidized which means it loses electrons and forms different oxides.

The explanation for the correct option:

(D) Lithium:

• Li=1s²2s¹.
  Between copper and lithium, the ionization energy of lithium will be lower because after losing one electron it will attain a noble gas configuration.
  Hence, lithium will show spontaneous combustion.

The explanation for the incorrect option:

(A) Phosphorus:

• Electronic configuration of P=1s²2s²2p⁶3s²3p³.
• In electronic configurations, we can see that phosphorus is stable because of half-filled p orbitals.
• Phosphorus is a non-metal which can undergo spontaneous combustion.

(B) Calcium:

• Electronic configuration of Ca=1s²2s²2p⁶3s²3p⁶4s².
• Calcium is stable because of fully-filled orbitals.

(C) Copper:

• Electronic configuration of Cu=1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰.
• Copper is stable because of fully-filled orbitals.
• Copper does not catch fire itself it requires heat of application.
• Hence it will not show spontaneous combustion.

Therefore option (D) is correct. i.e., lithium is a metal which can undergo spontaneous combustion.