Which of the following shows diagonal relationship with B?
B Si
C Mg

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Hint: Try to figure out what is the diagonal relationship. From the name of the relationship, we can say that it is shown by diagonally opposite elements. Think about which period elements which show the diagonal relationship.

Complete answer:
We know that in the periodic table some elements show some special kind of relationship called diagonal relationship. This relationship is shown by some of the second and third-period elements.
Second-period elements such as Lithium, Beryllium, Boron show a diagonal relationship with third-period elements. The element of the second period shows some properties similar to the diagonally downward element. So, this relationship is called a diagonal relationship.
Lithium and magnesium are diagonally related. Beryllium and aluminum are diagonally related. Boron and silicon are diagonally related.
Boron forms acidic oxide similar to silicon, unlike aluminum which forms amphoteric oxide. That’s why boron hydroxide is acidic whereas aluminum hydroxide is amphoteric.
Boron and silicon form many polymeric ions such as borates and silicates respectively by sharing oxygen atoms whereas aluminum forms no such polymeric ions.
Hydrides of boron and silicon are gases whereas aluminum hydrides are polymeric solids. Hydrolysis of boron and silicon hydrides is fast and they are highly inflammable.
Boron shows some relationship with silicon which is nothing but a diagonal relationship.

So, the correct answer is “Option B”.

Generally, first elements of s and p block elements deviate in some properties with the rest of the group. This is because of its small size. Due to their small size, these elements show high internuclear forces and sometimes high electron repulsions. That’s why the first elements deviate from some general properties.