What two metals from the lanthanides of the activity series will not generate hydrogen gass when treated with an acid?
To determine the metals from the lanthanides that will not generate hydrogen gas when treated with an acid, we need to consult the activity series for metals. Unfortunately, the lanthanides are not commonly listed in the activity series. The activity series usually includes metals like lithium, sodium, potassium, calcium, etc.
However, we can make an educated guess based on the general trends in the reactivity of metals. Generally, metals lower in the activity series react more readily with acids to produce hydrogen gas. So, the metals higher in the series are less likely to produce hydrogen gas when treated with an acid.
Considering this, two metals from the lanthanides that are less reactive and therefore less likely to generate hydrogen gas when treated with an acid are cerium (Ce) and praseodymium (Pr). However, it's important to note that this is a general assumption, and further research or specific experiments may be necessary for a definitive answer.