Explanation:

Let's break down the HDI ranks (2021-22) for these neighbouring countries of India, from lowest to highest:

- Bangladesh – Lowest among these, HDI rank around 129.

- Bhutan – Higher than Bangladesh, rank around 127.

- Sri Lanka – Higher HDI, rank near 73.

- Maldives – Highest HDI in the region, rank near 90.

So, in increasing order (lowest to highest HDI):

- Bangladesh (d) ? Bhutan (c) ? Sri Lanka (a) ? Maldives (b)

Let’s check the options:

- Option 1: b-a-d-c – Maldives, Sri Lanka, Bangladesh, Bhutan (incorrect order)

- Option 2: a-b-c-d – Sri Lanka, Maldives, Bhutan, Bangladesh (incorrect order)

- Option 3: b-a-c-d – Maldives, Sri Lanka, Bhutan, Bangladesh (incorrect order)

- Option 4: a-b-d-c – Sri Lanka, Maldives, Bangladesh, Bhutan (incorrect order)

But correct increasing order is: d-c-a-b (not among given options).