Answer: a. Material symbol
Explanation:
When talking about the Material symbols of Organizational Culture, those unspoken norms and behaviours that explain to you the type of Organization you are in are what are being referred to.
Materials symbols explain the type of culture in an organization by conveying information on the Equality level of the employees as well as the type of performance and behaviour expected of them.
They can be expressed through dress codes, company cars and even offices given to a certain cadre of Employees.
Seeing as the above scenario deals with the dress code, it most likely falls under an Organization's material symbols.