Question

how do we know if we have to find limiting reagent or not its not mention in question?​

Answer 1

$\huge\text{\underline{Answer}}$

$\bold{Limiting Reagent}$

when we have to find the limiting reactants the question gives hint by adding the reaction takes completely or incompletely.

Limiting reagents are those reagents which are present in limited quantities in a reaction.

For finding limiting reagents

$\bold{compare the mole of reagents after balancing the reaction}$

If the no. of mole is lesser than the given mole then it is excess reagents.

while, if the no. of mole is greater than the given mole it is limiting reagents.

hence, by comparing the no. of moles of reagents to given moles of reagents you can find which is the limiting reagents.