Question

“Li metal is used in photoelectric cells, while Cs is not used.” Answer whether the above statement is true or false. If true enter $1$ , else enter $0$ .

Answer 1

Hint: Lithium has high ionisation enthalpy whereas Caesium has low ionisation enthalpy.
Size of lithium is smaller as compared to caesium.

Complete step by step answer:
Caesium is an element with the symbol Cs. The atomic number of Cs is $55$.
Lithium is an element with the symbol Li. The atomic number of Li is $3$.
When alkali metals are exposed to light, they lose electrons. This is called the photoelectric effect. As Li is smaller in size, the electrons present are strongly held by the nucleus and therefore, requires high energy to lose an electron. Also, we know that ionisation enthalpy of lithium is high. Therefore, Li requires a large amount of energy to lose electrons.
Whereas on the other hand, due to low ionisation energy of Cs and large size, it can easily lose electrons. On exposure to light, caesium can easily emit electrons. But in case of Lithium, due to high ionisation enthalpy of lithium, it is very difficult to lose electrons. Therefore, we cannot use Li in photoelectric cells.
Hence, after studying the above concepts, we can say that lithium cannot lose electrons easily whereas Caesium can lose electrons easily.
Therefore, we can say that we can use Cs metal in photoelectric cells, but cannot use Li.
Hence, the correct answer is $0$ i.e. false.

Note:
Another element which can be used in photoelectric cells is potassium as ionisation enthalpy of potassium is also low.ionization energy or ionisation energy, is the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule.