What constitutes sex discrimination in the workplace?

Sex discrimination in the workplace occurs when an individual is treated unfavorably because of their sex or gender. The situation described in the correct answer highlights a specific instance of discrimination: not promoting a woman to an executive position solely because of her gender. This reflects a bias against women, indicating that her qualifications and capabilities are being overlooked due to her sex, which is a clear violation of equal opportunity principles.

In terms of the other options, they do not encapsulate the essence of sex discrimination as defined by employment laws and ethical standards. Different wages for the same job based on job performance does not constitute sex discrimination since it is based on performance, not gender. Firing employees without cause may be unethical but does not specifically relate to discrimination based on gender unless it can be shown that the firing was due to the individual’s sex. Hiring more women than men in a company isn't inherently discriminatory; it can reflect an effort to balance gender representation in the workforce. Thus, the focus must be on the treatment based on gender, which is clearly demonstrated in the correct answer.