What is the correct sequence of tributaries of the river Ganga from West to East ?

Correct — A, (a) Yamuna, Ghaghara, Son, Gandak and Kosi.

The question asks for the order of the CONFLUENCES — the points at which each tributary meets the Ganga — read from west to east, which is the direction in which the Ganga itself flows across the northern plain. Fix each confluence to a place and the sequence settles itself.

YAMUNA joins at Prayagraj, in Uttar Pradesh. It is the westernmost of the five by a long way, and it is the Ganga's longest tributary. GHAGHARA joins near Revelganj, close to Chhapra in Saran district, Bihar. Rising in Tibet and known as the Karnali in Nepal, it is the Ganga's largest tributary by volume of water. SON joins near Maner, just west of Patna. It rises near Amarkantak in Chhattisgarh and comes up from the south, making it the principal right-bank tributary of this group. GANDAK joins at Sonepur, opposite Patna, a little downstream of the Son confluence. It is the Narayani in Nepal. KOSI joins near Kursela in Katihar district, far to the east. It is the Sapta Kosi in Nepal and is called the Sorrow of Bihar for its habit of shifting its channel across the plain.

So the confluences run Prayagraj, then Chhapra, then Maner, then Sonepur, then Kursela — Yamuna, Ghaghara, Son, Gandak, Kosi. That is option (a).

Two of the four options open with Ghaghara, and both are wrong for the same reason: the Yamuna meets the Ganga far upstream in Uttar Pradesh, several hundred kilometres west of any Bihar confluence, so nothing on this list can come before it. That single fact halves the option set at once.

The real discrimination is then between (a) and (c), which agree on Yamuna and Ghaghara and disagree on the order of Son and Gandak. The Son enters just WEST of Patna and the Gandak just east of it, at Sonepur, so the Son comes first. Anchoring both to Patna is the cleanest way to hold the pair: the Son is the river you cross before Patna coming from the west, the Gandak the one that comes down opposite it.

Why the others are wrong

• (b)Ghaghara, Yamuna, Gandak, Kosi and Son — Wrong at both ends. It opens with the Ghaghara, whose confluence is near Chhapra in Bihar, ahead of the Yamuna, whose confluence is at Prayagraj in Uttar Pradesh — several hundred kilometres further west. And it closes with the Son, which enters just west of Patna, after the Kosi, which enters near Kursela in Katihar district, far to the east. Only the middle of the sequence, Gandak before Kosi, is right. The option would suit a candidate ordering the rivers by size or by fame rather than by the position of their confluences.
• (c)Yamuna, Ghaghara, Gandak, Son, and Kosi — The most dangerous option on the page, because it is correct except for one transposition: it puts the Gandak before the Son. The Son joins the Ganga near Maner, just west of Patna; the Gandak joins at Sonepur, opposite Patna and downstream of the Son. So the true order is Son, then Gandak. The transposition is easy to make because the Son is a right-bank tributary flowing up from the Chhattisgarh plateau while the other four in the answer come down from the Himalaya, so a candidate sorting the Himalayan rivers correctly may drop the Son into the wrong slot. This option alone carries a serial comma — 'Gandak, Son, and Kosi' — where the other three print 'X and Y' without one; that is the Commission's own inconsistency and is not a signal about the answer.
• (d)Ghaghara, Yamuna, Kosi, Gandak and Son — The furthest from the answer. Like option (b) it places the Ghaghara ahead of the Yamuna, which reverses the two westernmost confluences. It then puts the eastern end of the sequence almost exactly backwards: Kosi, whose confluence near Kursela is the easternmost of the five, is placed third, and the Son, which joins just west of Patna, is placed last. Three of the five positions are wrong. It functions as the option a candidate reaches for when no confluence has been fixed to a place at all.

The Ganga system is best learned as a list of CONFLUENCES rather than as a list of rivers, because that is what sequencing questions test.

LEFT BANK, all descending from the Himalaya: Ramganga, Gomti, GHAGHARA (Karnali in Nepal), GANDAK (Narayani in Nepal), Burhi Gandak, KOSI (Sapta Kosi), Mahananda. RIGHT BANK, mostly rising on the peninsular plateau: YAMUNA — itself Himalayan — then SON, Punpun, Falgu, Kiul, Ajay and Damodar.

Reading west to east, the principal confluences fall in this order: Ramganga near Kannauj, Yamuna at Prayagraj, Gomti in Ghazipur district, Ghaghara near Chhapra, Son near Maner just west of Patna, Gandak at Sonepur opposite Patna, Burhi Gandak near Khagaria, Kosi near Kursela, and Mahananda in Katihar district before the river turns south into West Bengal.

Three facts about individual rivers recur in questions and are worth separating carefully, because they are easy to blur into one another. The YAMUNA is the LONGEST tributary. The GHAGHARA is the LARGEST by volume of water. The KOSI is the most destructive, notorious for shifting its course westward across north Bihar over the last two centuries, which is why it is called the Sorrow of Bihar. The SON is the odd one out in this group by direction of approach: it rises near Amarkantak in Chhattisgarh — the same upland that gives rise to the Narmada — and flows north-east into the Ganga, so it belongs to peninsular drainage rather than Himalayan.

The general technique for any river-sequencing question is to convert each river into a TOWN and then order the towns. Rivers are hard to place from memory; Prayagraj, Chhapra, Patna and Katihar are not.

Key facts

• West-to-east order of the five confluences: Yamuna at Prayagraj, Ghaghara near Chhapra, Son near Maner just west of Patna, Gandak at Sonepur opposite Patna, Kosi near Kursela in Katihar district.
• The Yamuna is the Ganga's longest tributary; the Ghaghara is its largest by volume of water.
• The Son rises near Amarkantak in Chhattisgarh, is about 784 km long, and joins the Ganges near Maner in Patna district, just west of Patna.
• The Ghaghara is the Karnali in Nepal, the Gandak is the Narayani, and the Kosi is the Sapta Kosi.
• The Kosi is called the Sorrow of Bihar for its shifting channel across the north Bihar plain.
• Left-bank tributaries are Himalayan — Ramganga, Gomti, Ghaghara, Gandak, Burhi Gandak, Kosi, Mahananda; right-bank ones other than the Yamuna are largely peninsular — Son, Punpun, Kiul, Ajay, Damodar.

Common traps

• Ordering by size or by fame instead of by the position of the confluence, which is what the stem asks for.
• Placing the Ghaghara before the Yamuna. The Yamuna joins at Prayagraj in Uttar Pradesh, far west of any Bihar confluence.
• Transposing the Son and the Gandak. The Son enters just west of Patna, the Gandak at Sonepur opposite it, so Son comes first.
• Missing the direction. The stem specifies west to east, and reading it as east to west inverts the whole answer.

• practice — not a real PYQ

  Which of the following is the largest tributary of the Ganga by volume of water ?

  • (a)Yamuna
  • (b)Ghaghara
  • (c)Gandak
  • (d)Kosi

  Answer(b) Ghaghara — known as the Karnali in Nepal, it contributes the greatest volume of water of any Ganga tributary and joins near Chhapra in Saran district, Bihar. The Yamuna is the longest tributary, which is a different superlative and the commonest confusion in this pair.

• practice — not a real PYQ

  The Son, a tributary of the Ganga, rises near

  • (a)Gangotri in Uttarakhand
  • (b)Amarkantak in Chhattisgarh
  • (c)the Mahabaleshwar plateau in Maharashtra
  • (d)Mount Kailash in Tibet

  Answer(b) Amarkantak in Chhattisgarh — the Son rises on the Amarkantak upland, the same source region as the Narmada, and flows north-east for about 784 km to join the Ganges near Maner just west of Patna. That peninsular origin is why it approaches the Ganga from the south, unlike the Himalayan tributaries around it.