5
The expression is formed only by one operand (the constant 5).
alfa
The expression is formed by one operand (the variable alfa)
a+2
The expression contains two operands (the variable a and the constant 2) and the binary operator +.
a*(b+1)
The expression contains two operands (the variable a and the expression written between round parentheses (b+1) ) connected by the binary arithmetic operator *.