1st row or nth row of the table

How can I select 1st row or nth row of the table.

select 1,2,3,4,5 from tablex
where
rownum<=1
minus
select 1,2,3,4,5 from tablex
where
rownum<1

this will return 1st row and subsequently change the values for the N th row..

Rgds

1.
Concept of SQL not garantee, then two some queries:
select * from a;
get equal order of rows.
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In this case:
select 1,2,3,4,5 from tablex
where
rownum<=1
minus
select 1,2,3,4,5 from tablex
where
rownum<1

may be works correctly, may be not.
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2.
What do u mean ("1/n row from table") ?
a) 1/n row in "phizical" order of store (u should use ROWID as order parameter)
b) 1/n row in some order (u should use FIELD_NAME as order parameter)