How to take backup of a table on a different schema in PostgreSQL

Please let us know in PostgreSQL how we can take backup of a table on a
different schema. We have db named "geopostgrest" and under Schema named
"1" (Not inside Public Schema) we need to take backup of table "activity"

Please see the following:

postgres=# \c geopostgrest
You are now connected to database "geopostgrest" as user "postgres".
geopostgrest=# \dt
No relations found.
geopostgrest=# \dt 1.
List of relations
Schema | Name | Type | Owner
--------+---------------------------------+-------+----------
1 | activity | table | postgres

We tried the following command but its not working.

pg_dump -U postgres -n1 -d geopostgrest -t activity -f activity_05-08-2015.sql

pg_dump: No matching tables were found

We are using PostgreSQL 9.4.4 and Ubuntu 14.04.2 LTS

Can any one please help us on it

Thanks