{"questions":[{"id":"mdcat-chem-atom-01","v":1,"subject":"chemistry","chapter":"atomic-structure","seed":true,"difficulty":1,"stem":"The maximum number of electrons that the third shell (n = 3) can hold is:","options":["8","18","32","9"],"answer":1,"explain":{"en":"A shell can hold at most 2n² electrons. For n = 3 that is 2 × 3² = 18 (3s² 3p⁶ 3d¹⁰).","ur":"کوئی شیل زیادہ سے زیادہ 2n² الیکٹران رکھ سکتا ہے۔ n = 3 کے لیے 2 × 3² = 18 (3s² 3p⁶ 3d¹⁰)۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-02","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":1,"stem":"How many orbitals are there in a d-subshell?","options":["3","7","1","5"],"answer":3,"explain":{"en":"For a d-subshell, l = 2, and the magnetic quantum number takes 2l + 1 = 5 values, so there are five d orbitals holding up to 10 electrons.","ur":"d سب شیل کے لیے l = 2 ہے اور میگنیٹک کوانٹم نمبر کی 2l + 1 = 5 قیمتیں ہیں، اس لیے پانچ d آربیٹل ہیں جن میں 10 تک الیکٹران آتے ہیں۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-03","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":1,"stem":"The neutron was discovered by:","options":["J. J. Thomson","Ernest Rutherford","James Chadwick","Niels Bohr"],"answer":2,"explain":{"en":"James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles. Thomson discovered the electron, and Rutherford's gold-foil experiment revealed the nucleus.","ur":"جیمز چیڈوک نے 1932 میں بیریلیم پر الفا ذرات کی بوچھاڑ سے نیوٹران دریافت کیا۔ تھامسن نے الیکٹران اور رتھرفورڈ نے نیوکلیئس دریافت کیا۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-04","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":2,"stem":"Which quantum number describes the orientation of an orbital in space?","options":["Magnetic quantum number","Principal quantum number","Azimuthal quantum number","Spin quantum number"],"answer":0,"explain":{"en":"The magnetic quantum number (m) gives the orientation of an orbital. The principal number (n) gives the shell and size, the azimuthal number (l) the subshell and shape, and the spin number (s) the electron's spin.","ur":"میگنیٹک کوانٹم نمبر (m) آربیٹل کی سمت بتاتا ہے۔ پرنسپل نمبر (n) شیل اور سائز، ازیمیوتھل نمبر (l) سب شیل اور شکل، اور اسپن نمبر الیکٹران کا گھماؤ بتاتا ہے۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-05","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":3,"stem":"The ground-state electronic configuration of chromium (Z = 24) is:","options":["[Ar] 3d⁴ 4s²","[Ar] 3d⁶","[Ar] 3d⁵ 4s¹","[Ar] 4s² 4p⁴"],"answer":2,"explain":{"en":"Chromium is an exception to the simple filling order: a half-filled 3d subshell (3d⁵) with 4s¹ is more stable than 3d⁴ 4s². Copper is a similar exception ([Ar] 3d¹⁰ 4s¹).","ur":"کرومیم عام ترتیب سے مستثنیٰ ہے: آدھا بھرا 3d سب شیل (3d⁵) اور 4s¹ زیادہ مستحکم ہے بجائے 3d⁴ 4s² کے۔ کاپر بھی ایسا ہی استثنا ہے ([Ar] 3d¹⁰ 4s¹)۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-06","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":1,"stem":"Isotopes of an element have the same number of:","options":["Neutrons","Protons","Nucleons","Mass units"],"answer":1,"explain":{"en":"Isotopes have the same atomic number (protons) but different numbers of neutrons, so their mass numbers differ. For example, carbon-12 and carbon-14 both have 6 protons.","ur":"آئسوٹوپس کا ایٹمی نمبر (پروٹان) ایک ہوتا ہے مگر نیوٹران مختلف، اس لیے ماس نمبر مختلف ہوتا ہے۔ مثلاً کاربن-12 اور کاربن-14 دونوں میں 6 پروٹان ہیں۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-07","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":2,"stem":"\"No two electrons in an atom can have the same set of four quantum numbers.\" This is:","options":["Hund's rule","The Aufbau principle","Heisenberg's uncertainty principle","Pauli's exclusion principle"],"answer":3,"explain":{"en":"Pauli's exclusion principle means an orbital holds at most two electrons, with opposite spins. Hund's rule is about filling degenerate orbitals singly first; the Aufbau principle is about filling lower-energy orbitals first.","ur":"پالی کے اصولِ اخراج کا مطلب ہے کہ ایک آربیٹل میں زیادہ سے زیادہ دو الیکٹران مخالف اسپن کے ساتھ آ سکتے ہیں۔ ہنڈ کا اصول برابر توانائی والے آربیٹلز کو پہلے اکیلے بھرنے کا ہے۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"},{"id":"mdcat-chem-atom-08","v":1,"subject":"chemistry","chapter":"atomic-structure","difficulty":2,"stem":"According to the Aufbau (n + l) rule, which subshell fills immediately after 4s?","options":["4p","3d","4d","5s"],"answer":1,"explain":{"en":"Subshells fill in order of increasing n + l. 4s has n + l = 4; 3d has 3 + 2 = 5 and 4p has 4 + 1 = 5. With equal n + l, the lower n fills first, so 3d comes before 4p.","ur":"سب شیل n + l کی بڑھتی ترتیب سے بھرتے ہیں۔ 4s کا n + l = 4؛ 3d کا 5 اور 4p کا بھی 5۔ برابر ہو تو کم n والا پہلے بھرتا ہے، اس لیے 3d، 4p سے پہلے۔"},"source":{"kind":"parcha-original"},"status":"sample","exam":"mdcat"}]}