A look at the queries and how Oracle Database handles data type conversion:
A: This statement takes a substring of the JOIN_DATE column. Since JOIN_DATE is a DATE type and SUBSTR function expects a string, implicit conversion will occur from DATE to string based on the NLS_DATE_FORMAT setting. However, this will not require explicit conversion in the query itself.
B: This statement tries to add '20' to JOIN_DATE. Oracle Database does not support adding a string to a DATE implicitly. An explicit conversion of '20' to a number is required, or using the INTERVAL keyword to add days or years as appropriate.
C: This statement concatenates the date with an empty string and the salary. The database will implicitly convert the JOIN_DATE from a DATE to a string using the NLS_DATE_FORMAT setting and then perform the concatenation.
D: This query attempts to compare a DATE column with a string literal '*10-02-2018'. An explicit conversion using TO_DATE is needed to convert the string to a DATE data type with the appropriate date format mask. In this case, because the string does not follow the NLS_DATE_FORMAT 'DD-MON-YY', it will not be implicitly converted correctly.
E: This statement adds '120.50' to SALARY. Oracle Database will implicitly convert the string '120.50' to a number before performing the arithmetic addition, as SALARY is a NUMBER data type.