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NEET Full Mock Test: Practice Test 9

Question paper with answer key. Selection Pro

Q1. Two long parallel wires carrying equal currents $I$ in opposite directions are separated by a distance $d$. The magnetic field intensity at the midpoint between the wires is:
  1. Zero
  2. $\frac{\mu_0 I}{\pi d}$
  3. $\frac{2\mu_0 I}{\pi d}$
  4. $\frac{\mu_0 I}{2\pi d}$

Answer: (C) $\frac{2\mu_0 I}{\pi d}$

At the midpoint, fields due to both wires point in the same direction. $B_{net} = \frac{\mu_0 I}{2\pi (d/2)} + \frac{\mu_0 I}{2\pi (d/2)} = \frac{\mu_0 I}{\pi d} + \frac{\mu_0 I}{\pi d} = \frac{2\mu_0 I}{\pi d}$.

Q2. The work function of a photosensitive surface is $3.3\text{ eV}$. The threshold frequency for photoelectric emission is ($h = 6.6 \times 10^{-34}\text{ J\cdot s}$):
  1. $8.0 \times 10^{14}\text{ Hz}$
  2. $4.0 \times 10^{14}\text{ Hz}$
  3. $1.2 \times 10^{15}\text{ Hz}$
  4. $2.5 \times 10^{14}\text{ Hz}$

Answer: (A) $8.0 \times 10^{14}\text{ Hz}$

$\Phi = h \nu_0 \implies \nu_0 = \frac{3.3 \times 1.6 \times 10^{-19}\text{ J}}{6.6 \times 10^{-34}\text{ J\cdot s}} = 8.0 \times 10^{14}\text{ Hz}$.

Q3. An ideal gas expands adiabatically from volume $V$ to $8V$. If the ratio of specific heats is $\gamma = 5/3$, the ratio of initial to final pressure is:
  1. $8$
  2. $16$
  3. $32$
  4. $64$

Answer: (C) $32$

For an adiabatic process, $P_1 V_1^{\gamma} = P_2 V_2^{\gamma} \implies \frac{P_1}{P_2} = \left(\frac{V_2}{V_1}\right)^{\gamma} = (8)^{5/3} = (2^3)^{5/3} = 2^5 = 32$.

Q4. In a $p-n$ junction diode, the thickness of the depletion layer is of the order of:
  1. $1\text{ cm}$
  2. $1\text{ mm}$
  3. $10^{-6}\text{ m}$
  4. $10^{-10}\text{ m}$

Answer: (C) $10^{-6}\text{ m}$

The width of the depletion region in a semiconductor $p-n$ junction is typically on the order of $10^{-6}\text{ m}$ ($1\ \mu\text{m}$).

Q5. A body of mass $m$ is moving in a circular path of radius $r$ with constant speed $v$. The work done by the centripetal force during one complete revolution is:
  1. $\frac{m v^2}{r} \cdot 2\pi r$
  2. Zero
  3. $\frac{1}{2} m v^2$
  4. $m v^2$

Answer: (B) Zero

The centripetal force acts perpendicular to the direction of motion at every instant ($ \theta = 90^\circ$). Hence, work done $W = F d \cos(90^\circ) = 0$.

Q6. The speed of electromagnetic waves in a vacuum is equal to:
  1. $\sqrt{\mu_0 \varepsilon_0}$
  2. $\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$
  3. $\frac{\mu_0}{\varepsilon_0}$
  4. $\sqrt{\frac{\mu_0}{\varepsilon_0}}$

Answer: (B) $\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$

Maxwell proved that the velocity of electromagnetic radiation in free space is given by $c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}}$.

Q7. A simple pendulum of length $L$ has a time period $T$. If the acceleration due to gravity increases by $4\%$, its time period will:
  1. Increase by $2\%$
  2. Decrease by $2\%$
  3. Increase by $4\%$
  4. Decrease by $4\%$

Answer: (B) Decrease by $2\%$

$T = 2\pi \sqrt{\frac{L}{g}} \implies \frac{\Delta T}{T} = -\frac{1}{2}\frac{\Delta g}{g} = -\frac{1}{2}(4\%) = -2\%$. The time period decreases by $2\%$.

Q8. The focal length of an objective lens of an astronomical telescope is $100\text{ cm}$ and that of the eyepiece is $5\text{ cm}$. The magnifying power for normal adjustment is:
  1. $20$
  2. $500$
  3. $105$
  4. $95$

Answer: (A) $20$

Magnifying power in normal adjustment is $m = \frac{f_o}{f_e} = \frac{100}{5} = 20$.

Q9. Which alkali metal hydroxide is the most basic in nature?
  1. $\text{LiOH}$
  2. $\text{NaOH}$
  3. $\text{KOH}$
  4. $\text{CsOH}$

Answer: (D) $\text{CsOH}$

Down group 1, ionic radius increases, reducing $M-OH$ bond energy. Thus, $\text{CsOH}$ dissociates most readily, making it the most basic.

Q10. The shape of $\text{PCl}_5$ molecule in the gas phase according to VSEPR theory is:
  1. Trigonal bipyramidal
  2. Square pyramidal
  3. Octahedral
  4. Tetrahedral

Answer: (A) Trigonal bipyramidal

$\text{PCl}_5$ has 5 bond pairs and $sp^3d$ hybridization, yielding a trigonal bipyramidal shape.

Q11. Which of the following ampicillin/amine derivatives reacts with Hinsberg's reagent to give a product insoluble in alkali?
  1. Primary amine
  2. Secondary amine
  3. Tertiary amine
  4. Quaternary ammonium salt

Answer: (B) Secondary amine

Secondary amines react with Hinsberg's reagent (benzenesulfonyl chloride) to form $N,N$-dialkylbenzenesulfonamides, which lack an acidic hydrogen and are insoluble in aqueous $\text{KOH}$.

Q12. The oxidation number of Nickel in $[\text{Ni(CO)}_4]$ is:
  1. $0$
  2. $+2$
  3. $+4$
  4. $-2$

Answer: (A) $0$

Carbon monoxide ($\text{CO}$) is a neutral ligand. $x + 4(0) = 0 \implies x = 0$.

Q13. For a reaction to be spontaneous at all temperatures, the conditions must be:
  1. $\Delta H < 0$ and $\Delta S > 0$
  2. $\Delta H > 0$ and $\Delta S < 0$
  3. $\Delta H < 0$ and $\Delta S < 0$
  4. $\Delta H > 0$ and $\Delta S > 0$

Answer: (A) $\Delta H < 0$ and $\Delta S > 0$

Since $\Delta G = \Delta H - T\Delta S$, when $\Delta H$ is negative and $\Delta S$ is positive, $\Delta G$ is always negative at any temperature.

Q14. Which halogen forms only one oxoacid ($ HOF$)?
  1. Fluorine
  2. Chlorine
  3. Bromine
  4. Iodine

Answer: (A) Fluorine

Fluorine is highly electronegative and lacks $d$-orbitals, forming only one oxoacid, fluoric(I) acid ($\text{HOF}$).

Q15. The standard reduction potentials of three metals $A$, $B$, and $C$ are $+0.34\text{ V}$, $-0.76\text{ V}$, and $-2.37\text{ V}$ respectively. Their reducing power order is:
  1. $A > B > C$
  2. $C > B > A$
  3. $B > C > A$
  4. $A > C > B$

Answer: (B) $C > B > A$

More negative reduction potential corresponds to a stronger reducing agent. Hence order is $C > B > A$.

Q16. Ozonolysis of 2-methylbut-2-ene produces:
  1. Propanone and Ethanal
  2. Ethanal and Methanal
  3. Propanone and Methanal
  4. Butanone and Ethanal

Answer: (A) Propanone and Ethanal

Cleaving the double bond in $(\text{CH}_3)_2\text{C}=\text{CH}-\text{CH}_3$ via ozonolysis gives propanone ($(\text{CH}_3)_2\text{C}=\text{O}$) and ethanal ($\text{CH}_3\text{CHO}$).

Q17. In photorespiration (C2 cycle), the organelles involved in sequential order are:
  1. Chloroplast, Peroxisome, Mitochondrion
  2. Chloroplast, Mitochondrion, Peroxisome
  3. Peroxisome, Chloroplast, Mitochondrion
  4. Mitochondrion, Peroxisome, Chloroplast

Answer: (A) Chloroplast, Peroxisome, Mitochondrion

Photorespiration occurs in three cell organelles in sequence: Chloroplast $\rightarrow$ Peroxisome $\rightarrow$ Mitochondrion.

Q18. Genetic code is described as 'degenerate' because:
  1. One codon codes for more than one amino acid
  2. More than one codon can code for a single amino acid
  3. Codons overlap during translation
  4. It varies between prokaryotes and eukaryotes

Answer: (B) More than one codon can code for a single amino acid

Degeneracy means that most amino acids are specified by more than one codon (e.g., 6 different codons code for Leucine).

Q19. The functional cross-section of plant tissue responsible for translocation of organic solutes (sucrose) is:
  1. Xylem vessels
  2. Sieve tube elements
  3. Sclereids
  4. Tracheids

Answer: (B) Sieve tube elements

Sieve tubes along with companion cells in phloem conduct organic food from leaves to sink tissues.

Q20. Which of the following is a non-symbiotic (free-living) nitrogen-fixing bacterium?
  1. Rhizobium
  2. Azotobacter
  3. Frankia
  4. Anabaena azollae

Answer: (B) Azotobacter

*Azotobacter* and *Beijerinckia* are free-living aerobic nitrogen-fixing bacteria in soil.

Q21. The floral formula $\bigoplus \Phi K_{(5)} C_{(5)} A_5 \underline{G}_{(2)}$ belongs to which family?
  1. Fabaceae
  2. Solanaceae
  3. Liliaceae
  4. Brassicaceae

Answer: (B) Solanaceae

Solanaceae exhibits actinomorphic symmetry, fused calyx (5), fused corolla (5), 5 epipetalous stamens, and bicarpellary syncarpous superior ovary.

Q22. In recombinant DNA technology, plasmid vectors are useful because they:
  1. Are linear double-stranded RNA
  2. Replicate independently of genomic DNA
  3. Integrate into host chromosome permanently
  4. Lack origin of replication

Answer: (B) Replicate independently of genomic DNA

Plasmids are extra-chromosomal, autonomous, self-replicating circular double-stranded DNA molecules.

Q23. Which stage of cell division is characterized by the formation of synaptonemal complex?
  1. Leptotene
  2. Zygotene
  3. Pachytene
  4. Diplotene

Answer: (B) Zygotene

During zygotene stage of Prophase I, homologous chromosomes pair up (synapsis) mediated by synaptonemal complex.

Q24. The primary photosynthetic pigment present in all green plants that absorbs light in blue and red regions is:
  1. Chlorophyll a
  2. Chlorophyll b
  3. Carotenoids
  4. Xanthophylls

Answer: (A) Chlorophyll a

Chlorophyll a acts as the chief reaction-center pigment in light reaction of photosynthesis.

Q25. Which region of human brain acts as the primary center for regulating body temperature, hunger, and thirst?
  1. Cerebellum
  2. Thalamus
  3. Hypothalamus
  4. Medulla oblongata

Answer: (C) Hypothalamus

The hypothalamus contains centers that control body temperature, urge for eating (hunger), and drinking (thirst).

Q26. In human female, the corpus luteum is formed after ovulation from the remnants of:
  1. Primary follicle
  2. Graafian follicle
  3. Secondary oocyte
  4. Corpus albicans

Answer: (B) Graafian follicle

Following ovulation, the ruptured Graafian follicle transforms under LH influence into the endocrine structure called corpus luteum.

Q27. Which antibody class is most abundant in human blood serum and can cross the placenta?
  1. IgA
  2. IgM
  3. IgG
  4. IgE

Answer: (C) IgG

IgG is the most abundant immunoglobulin (~80%) and the only class capable of crossing the placental barrier.

Q28. Glomerular Filtration Rate (GFR) in a healthy human adult is approximately:
  1. $125\text{ mL/min}$ ($180\text{ L/day}$)
  2. $500\text{ mL/min}$
  3. $50\text{ mL/min}$
  4. $12.5\text{ L/day}$

Answer: (A) $125\text{ mL/min}$ ($180\text{ L/day}$)

Normal GFR in a healthy individual is around $125\text{ mL/minute}$, amounting to $180\text{ liters}$ per day.

Q29. The pacemaker of human heart that initiates action potentials spontaneously is:
  1. Atrioventricular Node (AVN)
  2. Sinoatrial Node (SAN)
  3. Bundle of His
  4. Purkinje fibers

Answer: (B) Sinoatrial Node (SAN)

SAN generates maximum action potentials ($70-75/\text{min}$) and sets the rhythm of heart contractions, acting as the pacemaker.

Q30. Which hormone acts on the collecting duct of kidney nephrons to increase water reabsorption?
  1. Oxytocin
  2. Anti-Diuretic Hormone (ADH / Vasopressin)
  3. Aldosterone
  4. Atrial Natriuretic Factor (ANF)

Answer: (B) Anti-Diuretic Hormone (ADH / Vasopressin)

ADH facilitates water reabsorption from distal parts of the tubule and collecting duct to prevent diuresis.

Q31. Cartilaginous joint in human skeleton is exemplified by:
  1. Sutures in skull
  2. Joint between adjacent vertebrae
  3. Shoulder joint (ball and socket)
  4. Knee joint (hinge)

Answer: (B) Joint between adjacent vertebrae

Joints between adjacent vertebrae in the vertebral column are cartilaginous joints permitting limited movement.

Q32. The enzyme carbonic anhydrase present in high concentrations in RBCs catalyzes the conversion of:
  1. $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$
  2. $\text{O}_2 + \text{Hb} \rightleftharpoons \text{HbO}_2$
  3. Glucose $\rightarrow$ Pyruvate
  4. Pepsinogen $\rightarrow$ Pepsin

Answer: (A) $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3$

Carbonic anhydrase speeds up the hydration of carbon dioxide into carbonic acid ($\text{H}_2\text{CO}_3$) for transport as bicarbonate ions.