In the context of the 'Trait Theory of Personality', which of the following statements is most appropriate and true regarding the scientific nature and measurement basis of the '16PF' (Sixteen Personality Factor Questionnaire) developed by psychologist Raymond Cattell and the types of traits classified by Gordon Allport—namely 'Cardinal', 'Central', and 'Secondary' traits?

Raymond Cattell studied personality using the statistical technique of 'Factor Analysis'. He distinguished between 'surface traits' (which are easily visible in external behavior) and 'source traits' (which are deep, fundamental, and enduring components of personality). Cattell developed the '16PF' (16 Personality Factor) questionnaire specifically to measure these source traits. Therefore, statement (b) is completely true.

Statements (a) and (c) are incorrect because, according to Allport, 'Cardinal traits' are extremely rare and dominate an individual's entire life (such as Gandhi's non-violence), whereas 'Central traits' are general and prominent characteristics that form the foundation of most individuals' personalities. Statement (d) is incorrect because the 16PF is an objective self-report questionnaire, not a projective technique.