Paramagnetic gas property in flue-gas analysis Which listed gas is the strongest paramagnetic species commonly encountered in combustion or process streams?

Introduction / Context:
Paramagnetism—the attraction of a substance toward a magnetic field—forms the basis of certain oxygen analyzers. Understanding which gases are strongly paramagnetic helps interpret analyzer selectivity and avoid cross-sensitivity issues in flue-gas monitoring and safety systems.

Given Data / Assumptions:

• Common combustion and process gases are considered.
• Paramagnetism arises from unpaired electrons in molecular orbitals.
• Instrument designs exploit magnetic susceptibility differences.

Concept / Approach:
Diatomic oxygen (O2) has two unpaired electrons in antibonding orbitals, making it strongly paramagnetic—much stronger than most other common gases. In contrast, carbon dioxide (CO2) is diamagnetic. Nitric oxide (NO) and nitrogen dioxide (NO2) are also paramagnetic, but their susceptibilities are lower and less consistently exploited for routine measurement than O2. Therefore, oxygen stands out as the strongest paramagnetic gas among the given options.

Step-by-Step Solution:

Verification / Alternative check:
Paramagnetic oxygen analyzers rely on O2's large magnetic susceptibility to physically deflect a measuring element or produce torque, confirming its dominance.

Why Other Options Are Wrong:

• CO2: Diamagnetic; repelled by magnetic fields.
• NO/NO2: Paramagnetic, but weaker and less universally used for paramagnetic detection than O2.

Common Pitfalls:
Assuming all oxidizers are strongly paramagnetic; susceptibility depends on electron configuration, not chemical reactivity.

Final Answer:
O2