In the English Grammar Profile, B1 point 44 in the category of PRONOUNS/substitution is defined as:
‘one’ after ‘which’ in indirect questions to refer to one of two or more options.
For example:
If I were to show you these two urban scenes, and I were to ask you which one is more beautiful, which one would you say?
*not all the examples are ‘indirect questions’ in the EGP examples.
A search in iWeb for:
which one * * *
1 WHICH ONE IS RIGHT FOR 2225
2 WHICH ONE OF THE FOLLOWING 1852
3 WHICH ONE IS THE BEST 1729
4 WHICH ONE IS BEST FOR 1458
5 WHICH ONE IS YOUR FAVORITE 931
6 WHICH ONE YOU WANT TO 809
7 WHICH ONE DO YOU THINK 735
8 WHICH ONE WORKS BEST FOR 643
9 WHICH ONE IS BETTER ? 633
10 WHICH ONE TO USE . 615
11 WHICH ONE IS IT ? 516
12 WHICH ONE ARE YOU ? 502
13 WHICH ONE IT IS . 491
14 WHICH ONE IS THE MOST 453
15 WHICH ONE WOULD YOU CHOOSE 429
16 WHICH ONE TO CHOOSE . 426
17 WHICH ONE OF THE TWO 421
18 WHICH ONE TO CHOOSE ? 349
19 WHICH ONE YOU CHOOSE , 334
20 WHICH ONE IS THE RIGHT 319
21 WHICH ONE DO YOU LIKE 316
22 WHICH ONE IS GOING TO 316
23 WHICH ONE YOU LIKE BEST 312
24 WHICH ONE IS BETTER FOR 306
25 WHICH ONE WOULD IT BE 306
26 WHICH ONE TO BUY . 305
27 WHICH ONE IS BETTER . 300
28 WHICH ONE WOULD YOU RECOMMEND 299
29 WHICH ONE OF THEM IS 283
30 WHICH ONE IS BEST ? 279
31 WHICH ONE TO GET . 270
32 WHICH ONE DO YOU WANT 263
33 WHICH ONE YOU LIKE THE 261
34 WHICH ONE OF THESE IS 259
35 WHICH ONE IT IS , 258
36 WHICH ONE WOULD BE THE 257
37 WHICH ONE SHOULD YOU CHOOSE 254
38 WHICH ONE WILL BE THE 252
39 WHICH ONE DO YOU PREFER 250
40 WHICH ONE OR MORE OF 234
41 WHICH ONE TO GO WITH 226
42 WHICH ONE IS BEST . 224
43 WHICH ONE BEST SUITS YOUR 222
44 WHICH ONE IS WHICH . 222
45 WHICH ONE TO GO FOR 222
46 WHICH ONE IT WAS . 209
47 WHICH ONE YOU PREFER . 206
48 WHICH ONE SHOULD I USE 205
49 WHICH ONE IS YOUR FAVOURITE 204
50 WHICH ONE IS CORRECT ? 202
1 DO N’T KNOW WHICH ONE 1347
2 TO FIGURE OUT WHICH ONE 1266
3 TO FIND OUT WHICH ONE 912
4 DO YOU KNOW WHICH ONE 740
5 DO NT KNOW WHICH ONE 726
6 CA N’T REMEMBER WHICH ONE 600
7 ‘M NOT SURE WHICH ONE 537
8 IF SO , WHICH ONE 524
9 DOES N’T MATTER WHICH ONE 460
10 LET US KNOW WHICH ONE 444
11 HELP YOU DECIDE WHICH ONE 381
12 YOU CAN CHOOSE WHICH ONE 310
PELIC STUDENT EXAMPLE:
Come and try their hamburgers,
then you can choose which one is special for you and know why I said that.
Spanish, Female, Level 3, Writing Class.
13 LET ME KNOW WHICH ONE 285
14 . NO MATTER WHICH ONE 283
15 , DEPENDING ON WHICH ONE 247
16 YOU CAN DECIDE WHICH ONE 238
17 DO N’T REMEMBER WHICH ONE 236
18 . NOT SURE WHICH ONE 215
19 AM NOT SURE WHICH ONE 214
20 . SO WHICH ONE 207
21 AND FIND OUT WHICH ONE 205
22 , AND SEE WHICH ONE 200
23 TRYING TO DECIDE WHICH ONE 199
24 DOES NT MATTER WHICH ONE 196
25 , NO MATTER WHICH ONE 190
26 THE EXTENT TO WHICH ONE 190
27 CA N’T DECIDE WHICH ONE 181
28 YOU TO DECIDE WHICH ONE 179
29 HARD TO KNOW WHICH ONE 178
30 AND FIGURE OUT WHICH ONE 177
31 HAVE NO IDEA WHICH ONE 170
32 IM NOT SURE WHICH ONE 160
33 DO I KNOW WHICH ONE 154
34 SO , WHICH ONE 154
35 A SITUATION IN WHICH ONE 153
36 WANT TO KNOW WHICH ONE 149
37 CAN YOU GUESS WHICH ONE 144
38 UP TO YOU WHICH ONE 142
39 DO NOT KNOW WHICH ONE 139
40 DO YOU DECIDE WHICH ONE 134
41 YOU NEVER KNOW WHICH ONE 134
42 DIFFICULT TO KNOW WHICH ONE 132
43 ( NOT SURE WHICH ONE 129
44 BUT NOT SURE WHICH ONE 126
45 ‘RE NOT SURE WHICH ONE 125
46 HARD TO DECIDE WHICH ONE 123
47 YOU CAN SEE WHICH ONE 121
48 DID N’T KNOW WHICH ONE 118
49 THE WAY IN WHICH ONE 116
50 . SO , WHICH ONE 115
A2:
correct, decide, following, guess, idea, if, let, matter, most, out, prefer, should, so, suits, sure, trying, way
B1:
depending on, figure, recommend, situation