To solve this problem, we need to determine the temperature at which pollen grains can be stored for several years in liquid nitrogen.$\newline$Liquid nitrogen is commonly used for cryopreservation due to its extremely low temperature, which helps in preserving biological samples by slowing down all biological processes.$\newline \bullet$Liquid nitrogen has a boiling point of approximately -196$^{\circ}$C.$\newline \bullet$At this temperature, biological samples, including pollen grains, can be stored for extended periods without degradation.$\newline$Let's analyze the options:$\newline \bullet$Option 1: -196$^{\circ}$C - This is the correct temperature for storing pollen grains in liquid nitrogen.$\newline \bullet$Option 2: -80$^{\circ}$C - This temperature is used for storing samples in ultra-low freezers, not in liquid nitrogen.$\newline \bullet$Option 3: -120$^{\circ}$C - This temperature is not typically associated with liquid nitrogen storage.$\newline \bullet$Option 4: -160$^{\circ}$C - This temperature is also not the boiling point of liquid nitrogen.$\newline$Therefore, the correct option is Option 1: -196$^{\circ}$C.