Which one of the following pairs (River - Direction) is not correctly matched?

1. A

   Amur river - North-East

   (a) Amur river - North-East. This pair claims that the Amur river flows in a north-easterly direction, which is factually correct as it forms part of the border between Russia and China before flowing east and northeast into the Sea of Okhotsk. Therefore, this option is correctly matched and is not the key.

2. B

   Syr Darya - North-West

   (b) Syr Darya - North-West. This pair claims that the Syr Darya river flows towards the north-west, which aligns with its actual course originating in the Tian Shan mountains and flowing northwest into the Aral Sea basin. Hence, this option is correctly matched and is not the key.

3. C

   Angara river - North

   (c) Angara river - North. This pair claims that the Angara river flows in a northerly direction, which is correct as it is the major outflow of Lake Baikal and flows north to join the Yenisei river in Siberia. Thus, this option is correctly matched and is not the key.

4. D

   Mekong river - South-West

   (d) Mekong river - South-West. This pair claims that the Mekong river flows in a south-westerly direction, which is incorrect because the Mekong flows primarily south and south-eastwards from the Tibetan Plateau through Southeast Asia into the South China Sea. Because this pair is incorrectly matched, it is the correct answer to the question.

Summary. Official key is (d) Mekong river - South-West. The question asks to identify the incorrectly matched river and flow direction pair among the given options. Options (a), (b), and (c) correctly represent the geographical flow directions of the Amur, Syr Darya, and Angara rivers respectively. On the other hand, the Mekong river flows towards the south and south-east, not south-west. Therefore, pair (d) is the only incorrect match and serves as the required answer.