BPSC 70th CCE Prelims General Studies · Question 40 of 143

Correct — A, Narmada. An odd-one-out question is answered by finding the single classifier that isolates exactly one item, and here that classifier is direction of drainage. The Narmada rises at the Narmada Kund on the Amarkantak plateau in Madhya Pradesh and runs roughly 1,312 km WESTWARD, down a rift valley between the Vindhya range to its north and the Satpura range to its south, before emptying into the Gulf of Khambhat, an arm of the Arabian Sea. Every other river in the list ends up in the Bay of Bengal. The Mahanadi rises at Sihawa in the Dhamtari district of Chhattisgarh and flows east for about 851 km to build a delta on the Odisha coast. The Tungabhadra is formed where the Tunga and the Bhadra meet at Koodli in Karnataka, flows east and north-east past Hampi, and joins the Krishna, which itself reaches the Bay of Bengal. The Penganga rises in the hills of northern Maharashtra and flows east into the Wardha, which unites with the Wainganga to form the Pranhita, which joins the Godavari — again, the Bay of Bengal. So three of the four drain to the east coast and one to the west, and the Narmada is the odd river out. Two further peculiarities reinforce the same answer. The Narmada occupies a tectonic rift valley — a down-faulted trough — rather than a valley it cut for itself, which it shares in India only with the Tapi. And because it enters the sea through a narrow, tide-scoured estuary near Bharuch rather than depositing on a shelving coast, it builds no delta, whereas the Mahanadi, the Krishna and the Godavari all have large deltas.

• (b)Tungabhadra — East-flowing and a tributary — the chief tributary of the Krishna, formed at Koodli by the union of the Tunga and the Bhadra and famous for flowing past the Vijayanagara capital at Hampi. It groups naturally with the Penganga as a tributary and with the Mahanadi as an east-flowing river, so no classifier isolates it.
• (c)Mahanadi — The most tempting wrong answer, because on the tributary test the Mahanadi looks unusual — like the Narmada it reaches the sea on its own. But that test splits the four two against two, since the Narmada and the Mahanadi are both independent while the Tungabhadra and the Penganga are both tributaries, and a classifier that produces two pairs cannot answer an odd-one-out question.
• (d)Penganga — The least familiar name in the set, which tempts candidates to pick it simply because they cannot place it. It is a sub-tributary of the Godavari — Penganga into Wardha, Wardha and Wainganga into the Pranhita, Pranhita into the Godavari — so it is east-draining like two of the others, and unfamiliarity is not a classifier.

Peninsular India tilts eastward, because the Western Ghats form a high edge close to the Arabian Sea while the land falls away gently towards the Bay of Bengal. The consequence is that almost all the large peninsular rivers — the Mahanadi, Godavari, Krishna, Kaveri and their tributaries — flow east, cut broad valleys and build deltas where they meet the Bay. Only two major rivers break the pattern, the Narmada and the Tapi, and they do so because they are not following the slope at all: both occupy ancient rift valleys, down-faulted troughs formed by tectonic movement, the Narmada between the Vindhyas and the Satpuras and the Tapi south of the Satpuras. Rivers confined to such troughs run fast and straight, carry their load out to sea, and open into estuaries rather than deltas — the standard exam formulation is that the west-flowing peninsular rivers have no deltas. Note that the reason is the coastal configuration and the confined valley, not any absence of sediment.

The method matters more than the fact here, because BPSC sets several odd-one-out items in every paper. Do not stop at the first difference you notice; test each candidate classifier and keep the one that leaves a 3–1 split. Independent river versus tributary gives 2–2 — Narmada and Mahanadi independent, Tungabhadra and Penganga tributaries — and is therefore useless. Length gives no natural break. Peninsular versus Himalayan makes all four the same. Direction of drainage gives 3–1 and picks the Narmada, and it is confirmed twice over by the rift-valley origin and the estuary. The single fact that decides the question is that the Narmada empties into the Gulf of Khambhat on the Arabian Sea while the other three, directly or through a parent river, reach the Bay of Bengal — so if you can trace the Penganga to the Godavari and the Tungabhadra to the Krishna, the question is finished.

• Narmada: rises at Narmada Kund, Amarkantak plateau, Madhya Pradesh; about 1,312 km long; flows WEST through a rift valley between the Vindhya and Satpura ranges into the Gulf of Khambhat
• Mahanadi: rises at Sihawa in Dhamtari district, Chhattisgarh; about 851 km; flows east and builds a delta on the Odisha coast; dammed at Hirakud
• Tungabhadra: formed at Koodli in Karnataka by the union of the Tunga and the Bhadra; the principal tributary of the Krishna, which drains to the Bay of Bengal; Hampi stands on its bank
• Penganga: a tributary of the Wardha, which joins the Wainganga to form the Pranhita, which joins the Godavari — a Bay of Bengal river at two removes
• The Narmada and the Tapi are India's two large rift-valley rivers and neither forms a delta; they discharge through estuaries into the Arabian Sea

• Classifying by 'independent river versus tributary', which splits this set 2–2 and cannot isolate anyone
• Picking the least familiar name — the Penganga here — instead of applying a test to all four
• Assuming west-flowing rivers carry no silt; they do, but the narrow rift valleys and the steep west coast give them estuaries instead of deltas

BPSC uses the bare 'which one is different' format with no hint about the criterion, so the work is in choosing the classifier — and the paper reuses the format across subjects, from rivers to letter groups. UPSC almost never asks an unqualified odd-one-out; it names the criterion in the stem, or tests the same drainage facts as a pair-matching item or an assertion-reason on why west-flowing rivers have no deltas.

• practice — not a real PYQ

  Which of the following pairs of rivers both flow westward into the Arabian Sea ?

  • (a)Narmada and Tapi
  • (b)Godavari and Krishna
  • (c)Mahanadi and Subarnarekha
  • (d)Kaveri and Penganga

  Answer(a) Narmada and Tapi — India's two large rift-valley rivers, both discharging through estuaries into the Gulf of Khambhat; all the other rivers listed drain to the Bay of Bengal.

• practice — not a real PYQ

  The Penganga river is a tributary of which of the following river systems ?

  • (a)Krishna
  • (b)Mahanadi
  • (c)Godavari
  • (d)Narmada

  Answer(c) Godavari — the Penganga joins the Wardha, the Wardha and Wainganga form the Pranhita, and the Pranhita joins the Godavari.