Periodic Classification Of Elements

Let's analyze the given statements one by one and determine the accuracy of each, to choose the most appropriate answer from the given options.

1. Statement (I): The 4f and 5f-series of elements are placed separately in the Periodic table to preserve the principle of classification.
   The 4f and 5f series refer to the lanthanides and actinides, respectively. These elements are placed separately at the bottom of the periodic table, below the main body of the table. This positioning is indeed done to maintain the neatness and clarity of the periodic table, ensuring that it does not become overly wide. By placing these series separately, the periodic nature and classification principles remain clearer and more manageable. Thus, Statement (I) is true.
2. Statement (II): s-block elements can be found in pure form in nature.
   s-block elements in the periodic table include the alkali metals and alkaline earth metals. These elements are highly reactive due to their propensity to lose electrons easily, which means that they readily form compounds rather than existing in their pure elemental forms in nature. For example, sodium and potassium are found as salts rather than in their metallic forms. Thus, Statement (II) is false.

Based on the analysis, the correct option is: Statement I is true but Statement II is false.