;WITH CTE as (select row_number() OVER(partition by Binder_no ORDER BY Binder_id)
    AS rn,office_id,Binder_id,Binder_no
    FROM [Rev_Binders])
    SELECT * FROM cte where rn = 1

Results:

rn	office_id	Binder_id	Binder_no
1	2105110 	10           	101
1	2105110	        12	           102
1	2105110 	14              103
1	2105110 	16           	104
1	2105110 	17           	105
1	2105110 	20           	106

CREATE TABLE [REV_BINDERS](
[OFFICE_ID] [int] NOT NULL,
[BINDER_ID] [int] NOT NULL,
[BINDER_NO] [varchar](7) NULL,
);
go

INSERT INTO [REV_BINDERS] 
([OFFICE_ID],[BINDER_ID],[BINDER_NO])
select 2105110,10,0101 union all
select 2105110,12,0102 union all
select 2105110,13,0102 union all
select 2105110,14,0103 union all
select 2105110,15,0103 union all
select 2105110,16,0104 union all
select 2105110,17,0105 union all
select 2105110,18,0105 union all
select 2105110,19,0105 union all
select 2105110,20,0106;
go

with emp as (
select
    OFFICE_ID,
    BINDER_ID,
    BINDER_NO,
    count(*) over (PARTITION BY OFFICE_ID, BINDER_NO) as BinderCnt
from
    REV_BINDERS )
select * from emp where BinderCnt = 1;

go

DROP TABLE [REV_BINDERS];
go

CREATE TABLE [REV_BINDERS](
[OFFICE_ID] [int] NOT NULL,
[BINDER_ID] [int] NOT NULL,
[BINDER_NO] [varchar](7) NULL,
);
go

INSERT INTO [REV_BINDERS] 
([OFFICE_ID],[BINDER_ID],[BINDER_NO])
select 2105110 , 1	,0101 union all
select 2105110	,2	,0102	union all
select 2105110	,3	,0103	union all
select 2105110	,4	,0104	union all
select 2105110	,5	,0105	union all
select 2105110	,6	,0108	union all
select 2101110	,261	,0101	union all
select 2101110	,262	,0102	union all
select 2101110	,263	,0103	union all
select 2101110	,264	,0104	union all
select 2101110	,265	,0105	union all
select 2101110	,266	,0106	

SELECT
    rb.OFFICE_ID,
    MAX(rb.BINDER_ID),
    MAX(rb.BINDER_NO)
FROM dbo.REV_BINDERS AS rb
GROUP BY
    rb.OFFICE_ID
ORDER BY
    rb.OFFICE_ID;

+-----------+------------------+------------------+
| OFFICE_ID | (No column name) | (No column name) |
+-----------+------------------+------------------+
|   2101110 |              266 |              106 |
|   2105110 |                6 |              108 |
+-----------+------------------+------------------+

CREATE TABLE [REV_BINDERS](
[OFFICE_ID] [int] NOT NULL,
[BINDER_ID] [int] NOT NULL,
[BINDER_NO] [varchar](7) NULL,
);
go

INSERT INTO [REV_BINDERS] 
([OFFICE_ID],[BINDER_ID],[BINDER_NO])
select 2105110 , 1	,0101 union all
select 2105110	,2	,0102	union all
select 2105110	,3	,0103	union all
select 2105110	,4	,0104	union all
select 2105110	,5	,0108	union all
select 2105110	,6	,0105	union all
select 2101110	,261	,0101	union all
select 2101110	,262	,0102	union all
select 2101110	,263	,0103	union all
select 2101110	,264	,0104	union all
select 2101110	,265	,0106	union all
select 2101110	,266	,0105

SELECT
    t.OFFICE_ID,
    t.BINDER_NO,
    t.BINDER_ID
FROM 
(
    SELECT
        rb.OFFICE_ID,
        rb.BINDER_NO,
        group_count = COUNT_BIG(*) OVER (PARTITION BY rb.BINDER_NO),
        rb.BINDER_ID
    FROM dbo.REV_BINDERS AS rb
) AS t
WHERE
    t.group_count = 1;

+-----------+-----------+-----------+
| OFFICE_ID | BINDER_NO | BINDER_ID |
+-----------+-----------+-----------+
|   2101110 |       106 |       265 |
|   2105110 |       108 |         5 |
+-----------+-----------+-----------+

SELECT
    rb.OFFICE_ID,
    rb.BINDER_NO,
    rb.BINDER_ID
FROM dbo.REV_BINDERS AS rb
WHERE
    EXISTS
    (
        SELECT * 
        FROM dbo.REV_BINDERS AS rb2
        WHERE
            rb2.BINDER_NO = rb.BINDER_NO
        GROUP BY
            rb2.BINDER_NO
        HAVING
            COUNT_BIG(*) = 1
    );

+-----------+-----------+-----------+
| OFFICE_ID | BINDER_NO | BINDER_ID |
+-----------+-----------+-----------+
|   2101110 |       106 |       265 |
|   2105110 |       108 |         5 |
+-----------+-----------+-----------+