can C# enums be declared as of bool type?

It says

The approved types for an enum are byte, sbyte, short, ushort, int, uint, long, or ulong.

enum (C# Reference)

if you need your enum to contain boolean data in addition to the enum constant's type value, you could add a simple attribute to your enum, taking a boolean value. Then you can add an extension method for your enum that fetches the attribute and returns its boolean value.

public class MyBoolAttribute: Attribute
{
        public MyBoolAttribute(bool val)
        {
            Passed = val;
        }

        public bool Passed
        {
            get;
            set;
        }
}

public enum MyEnum
{
        [MyBoolAttribute(true)]
        Passed,
        [MyBoolAttribute(false)]
        Failed,
        [MyBoolAttribute(true)]
        PassedUnderCertainCondition,

        ... and other enum values

}

/* the extension method */    
public static bool DidPass(this Enum en)
{
       MyBoolAttribute attrib = GetAttribute<MyBoolAttribute>(en);
       return attrib.Passed;
}

/* general helper method to get attributes of enums */
public static T GetAttribute<T>(Enum en) where T : Attribute
{
       Type type = en.GetType();
       MemberInfo[] memInfo = type.GetMember(en.ToString());
       if (memInfo != null && memInfo.Length > 0)
       {
             object[] attrs = memInfo[0].GetCustomAttributes(typeof(T),
             false);

             if (attrs != null && attrs.Length > 0)
                return ((T)attrs[0]);

       }
       return null;
}