How to access Package Public variable into SELECT Statement using EXECUTE IMMEDIATE?

CREATE OR REPLACE PACKAGE sample_pkg AS
g_var VARCHAR2(5);
END sample_pkg;

/

CREATE OR REPLACE PACKAGE BODY sample_pkg AS 
BEGIN
g_var := 'hello';
dbms_output.put_line(g_var);
END;

/

SELECT sample_pkg.g_var FROM dual;

error ORA-06553: PLS-221: 'G_VAR' is not a procedure or is undefined

Obviously, you cannot call an internal variable of a package like that, presumably might convert to this one

CREATE OR REPLACE PACKAGE sample_pkg AS
  g_var VARCHAR2(500) := 'hello';
  FUNCTION f_var( i_var VARCHAR2 DEFAULT g_var ) RETURN VARCHAR2;  
END sample_pkg;
/
CREATE OR REPLACE PACKAGE BODY sample_pkg AS      
  FUNCTION f_var( i_var VARCHAR2 DEFAULT g_var ) RETURN VARCHAR2 IS
  BEGIN  
    RETURN i_var;
  END;  
END;
/

and call like this :

SELECT sample_pkg.f_var FROM dual;

F_VAR
-----
hello

or this :

SET SERVEROUTPUT ON  
BEGIN
  DBMS_OUTPUT.PUT_LINE(sample_pkg.f_var);
END; 
/
hello

Edit : Indeed, not needed; you can alternatively call the statement by using EXECUTE IMMEDIATE as desired such as

DECLARE
   result VARCHAR2(89);
   i_val  VARCHAR2(89):='Hello World!';
BEGIN
   EXECUTE IMMEDIATE 'SELECT sample_pkg_.f_var(:prm1) FROM dual' INTO result USING i_val; 
  DBMS_OUTPUT.PUT_LINE(result);
END;
/