ANS:B - has better electron emissivity.

In TIG (Tungsten Inert Gas) welding, thoriated tungsten electrodes are used primarily because they have better electron emissivity. Thoriated tungsten electrodes contain a small percentage of thorium oxide (usually around 1-2%) added to tungsten metal. Thorium improves the electron emission characteristics of the tungsten electrode, making it easier to initiate and maintain the welding arc. This property is particularly advantageous in TIG welding, where a stable and consistent arc is essential for achieving high-quality welds. While thoriated tungsten electrodes may have slightly higher current-carrying capacity compared to pure tungsten electrodes, their primary advantage lies in their superior electron emissivity. Thoriated tungsten electrodes are not necessarily stronger than pure tungsten electrodes, and their strength is not a significant factor in their selection for TIG welding applications. Additionally, thoriated tungsten electrodes require special handling and precautions due to the radioactive nature of thorium, which is another consideration in their use. Therefore, the most relevant reason for using thoriated tungsten electrodes in TIG welding is their superior electron emissivity, which contributes to better arc stability and weld quality.