Question

Sodium and potassium have _____ melting point than aluminium.
A) Higher
B) Lower
C) Equal
D) Can’t say

Answer 1

Hint: We are given sodium, potassium and aluminium. All the three sodium, potassium and aluminium are metals. To solve this we must know the factors affecting the melting points of metals. Along with that we must know the position of sodium, potassium and aluminium in the periodic table.

 Complete answer:We are given three metals sodium, potassium and aluminium.
The metals sodium and potassium are alkali earth metals. The alkali metals belong to group 1 the periodic table.
-For group 1 and group 2, the trend in melting point is as follows: Down the group the melting point decreases. This is because down the group the atomic size increases. Increase in atomic size leads to weaker bonds between the atoms of the metals. As a result less amount of energy is required to break these bonds and cause them to melt.
-In group 1, sodium lies above potassium. Thus, the atomic size of sodium is smaller than that of potassium. Thus, the melting point of sodium is higher than that of potassium.
-Aluminium belongs to group 13 of the periodic table. Both sodium and aluminium belong to period 3 of the periodic table.
-The atomic size of elements decreases as we move from left to right in the periodic table.
Sodium lies on the left side while aluminium lies on the right side of the periodic table. Thus, the atomic size of aluminium is smaller than that of sodium.
-Decrease in atomic size leads to stronger bonds between the atoms of the metals. As a result more energy is required to break these bonds and cause them to melt.
Thus, aluminium has a higher melting point than sodium.
Thus, sodium and potassium have lower melting points than aluminium.

Thus, the correct option is (B).

Note:We know that melting point of an element is the energy required to change the element from solid state to liquid state. The melting points of metals are generally very high. The factor that affects the melting point of metals is the atomic size. The melting point varies inversely with the atomic size.