If atomic number of an element is 11, the correct name, symbol and valency are:
- (a)Lithium, Li, 1
- (b)Magnesium, Mg, 2
- (c)Boron, B, 3
- (d)Sodium, Na, 1
Correct — D, Sodium, Na, 1. Atomic number is the number of protons, and it fixes the element without ambiguity: 11 protons means sodium. Its symbol Na comes from the Latin natrium, one of a small group of elements whose symbols do not match their English names. The valency follows from the electron arrangement. Eleven electrons fill as 2, 8, 1 — two in the first shell, eight in the second, and a single electron left over in the third. That lone outer electron is loosely held, and sodium reaches the stable configuration of neon simply by losing it, forming Na⁺. Since one electron is involved in bonding, the valency is 1. Every part of the option therefore has to be checked, which is what makes this a three-way test rather than a one-way one: the name must match the atomic number, the symbol must match the name, and the valency must follow from the electron configuration.
- (a)Lithium, Li, 1 — Lithium is element 3, with configuration 2, 1. Its valency of 1 is right for lithium — and that is the trap, since sodium sits directly below it in Group 1 and shares the valency. Only the atomic number separates them here.
- (b)Magnesium, Mg, 2 — Magnesium is element 12, one place further on, with configuration 2, 8, 2 and valency 2. Choosing this means being off by a single proton.
- (c)Boron, B, 3 — Boron is element 5, configuration 2, 3, valency 3. Neither the atomic number nor the group is close to sodium's.
The atomic number Z is the number of protons in the nucleus and is what defines an element. In a neutral atom it is also the number of electrons, and those electrons occupy shells in a fixed order — up to 2 in the first, 8 in the second, 8 in the third for the light elements. The number of electrons in the outermost shell determines chemical behaviour: elements with one outer electron lose it readily and are the reactive alkali metals of Group 1; those with seven gain one and are the halogens; those with a full outer shell are the noble gases.
The efficient route through this item is to identify the element from Z first and only then check the rest of the option, because three of the four options name elements with the wrong atomic number and fall immediately. Writing out 2, 8, 1 is worth doing even when you already recognise sodium, because it is what justifies the valency and because the same working answers a whole family of questions. Two things are worth fixing in memory for the exam. First, the small set of symbols derived from Latin — Na for sodium (natrium), K for potassium (kalium), Fe for iron (ferrum), Cu for copper (cuprum), Ag for silver (argentum), Au for gold (aurum), Pb for lead (plumbum), Sn for tin (stannum) — since papers like to pair a name with the wrong symbol. Second, that Group 1 elements all share valency 1, so valency alone can never distinguish lithium from sodium; only the atomic number can.
- Atomic number is the number of protons and uniquely identifies the element; element 11 is sodium.
- Sodium's symbol Na derives from the Latin natrium.
- Sodium's electron configuration is 2, 8, 1 — a single electron in the outermost shell.
- Losing that one electron gives Na⁺, the stable configuration of neon, so sodium's valency is 1.
- Lithium (Z = 3) and sodium (Z = 11) are both Group 1 metals with valency 1, so valency cannot distinguish them.
- Magnesium is Z = 12 with configuration 2, 8, 2 and valency 2.
Identify from Z first; the rest of the option then either matches or it does not.
- Choosing lithium because its valency of 1 is correct — the valency matches, but the atomic number does not.
- Being off by one and picking magnesium at Z = 12.
- Pairing an element with the wrong symbol where the symbol comes from Latin.
As a combined name-symbol-valency item like this one, or split up — 'the element with atomic number X is', or 'the valency of sodium is'. Latin-derived symbols are asked in their own right.
No directly related past PYQ was found.
- practice — not a real PYQ
The electronic configuration 2, 8, 2 corresponds to which element?
- (a)Sodium
- (b)Magnesium
- (c)Neon
- (d)Calcium
Answer(b) Magnesium — twelve electrons in all, with two in the outermost shell, giving valency 2.
- practice — not a real PYQ
The chemical symbol K for potassium is derived from which Latin name?
- (a)Kalium
- (b)Natrium
- (c)Cuprum
- (d)Stannum
Answer(a) Kalium — as sodium's Na comes from natrium, copper's Cu from cuprum and tin's Sn from stannum.