Final answer:
The 14th Amendment's Equal Protection Clause makes it illegal for states to discriminate on the basis of race, sex, or religion, hence scenarios a, b, and c would be considered illegal. Discrimination based on age may be lawful under certain circumstances.
Step-by-step explanation:
The scenarios that would be considered illegal in light of the provisions of the 14th Amendment are denying citizens the right to vote based on race, implementing educational segregation based on gender, and taxing individuals differently based on their religious beliefs. The Equal Protection Clause of the 14th Amendment requires states to treat all residents equally under the law regardless of race, color, ethnicity, sex, gender, religion, and other attributes. Therefore, allowing discrimination in employment based on age could potentially be legal under certain conditions if there is a rational basis for the discrimination related to job performance or safety.
The provided scenarios, a, b, and c, explicitly violate the principles established by the 14th Amendment as they involve discrimination based on race, gender, and religion respectively, which is forbidden under the Equal Protection Clause. Scenario d, concerning age discrimination, requires additional context as laws like the Age Discrimination in Employment Act of 1967 offer some protections, but there are scenarios in which age can be a lawful hiring consideration (e.g., when age is a bona fide occupational qualification).