Krishna says, "Among the ๐ผ๐๐๐ฉ๐ฎ๐๐จ , I am Vishnu; I am radiating Sun and Moon (10.21). Among the Vedas, I am ๐๐๐ข๐ ๐๐๐๐ ; I am ๐๐๐จ๐ช๐ซ๐ (๐๐ฃ๐๐ง๐) ; among the senses, I am Mind ( ๐ข๐๐ฃ๐๐จ ); in creatures, I am Chetana (consciousness) (10.22). Of the ๐๐ช๐๐ง๐๐จ I am ๐๐๐๐ฃ๐ ๐๐ง๐ ; I am ๐๐ช๐๐๐ง๐ (10.23). I am ๐ฝ๐ง๐๐๐๐จ๐ฅ๐๐ฉ๐ ; among expanses of water, I am the ocean (10.24).
Krishna earlier said that HE is the ๐๐ฉ๐ข๐ (soul) in the heart of all beings (10.20) and gave a hierarchy that the ๐๐ฉ๐ข๐ is superior to ๐๐ช๐๐๐๐ (intellect); ๐๐ช๐๐๐๐ is superior to the mind; the mind is superior to the senses (3.42). But here he says HE is the mind among senses and this needs understanding.
It is said that 'the whole is greater than the sum of the parts'. As a whole two ears can bring a sense of direction of sound; two eyes together can produce depth perception. One way of looking at the mind is as a simple sum of its senses like ears, eyes etc. Another way is to look at it 'as a whole of senses' where together these senses can perceive far beyond what a sum of all senses can do. This is also known as 'beyond senses' or 'sixth sense' in the modern context. Krishna was referring to this sixth sense when he says HE is the mind among senses.
Krishna further says, "Among words, I am the ๐ผ๐ช๐ข (๐๐ข) ; among stationary objects, I am the Himalayas (10.25). Among all trees, I am the peepal tree; I am Narada; I am the ๐ข๐ช๐ฃ๐ ๐๐๐ฅ๐๐ก๐ (10.26). I am ๐ผ๐๐ง๐๐ซ๐๐ฉ๐ amongst all lordly elephants, and the king amongst humans" (10.27).
One common thread in all of the above is that out of the available options HE represents the greatest possibility of 'peak performance' like the water becoming the ocean. options HE represents the greatest possibility of 'peak performance' like the water becoming the ocean.