So, here are some questions along with their answers and explanations from all three subjects i.e. Physics, Chemistry, and Mathematics. Students must go through these questions and revise the most important topics of each subject before they appear in the exam. Practising these questions will help you perform well and obtain good marks in JEE Main Exam 2023.
Below are the important questions of JEE Main Exam:
Question 1: Select the correct stability order of the conformation /Rotamers/ Rotational isomers of Ethane Molecule
(a) Partially Eclipsed > Fully Eclipsed > Anti-staggered > Skew or Gouche
(b) Skew or Gouche > Partially Eclipsed > Fully Eclipsed > Anti-staggered
(c) Anti-staggered > Skew or Gouche > Partially Eclipsed > Fully Eclipsed
(d) Fully Eclipsed > Anti-staggered > Skew or Gouche > Partially Eclipsed
Solution:
The isomers which can be produced by the free rotation about single bond are known as conformation /Rotamers/ Rotational isomers and this phenomenon is called as conformational analysis
These isomers can be represented by
1. Sawhorse projection
2. Newman's projection formula
3. A staggered conformer is more stable than an eclipsed conformer as the latter involves unfavourable energy interactions between atoms.
4. In conformational analysis (energetics study of different rotational conformers or rotamers), structures are represented by *Newman projection * (atoms and bonds are viewed along the axis of rotation).
Hence, the correct answer is (c).
Question 2: As per IUPAC nomenclature, the name of the complex [Co (H2O)4(NH3 )2]C13 is
(a) tetraaquadiaminecobalt (III) chloride
(b) tetraaquadiamminecobalt (III) chloride
(c) diaminetetraaquacobalt (III) chloride
(d) diamminetctraaquacobalt (III) chloride
Solution:
First of all, the compound has complex positive part [Co(H2O)4(NH3)2]3+ therefore, according to IUPAC conventions, positive part will be named first. Secondly, in writing name of complex, ligands are named first in alphabetical order, irrespective of its charge, hence "ammine" will be written prior to "aqua".
NOTE: In alphabetical order, original name of ligands are considered not the initials of prefixes. Also, special precaution should be taken in spelling name of NH3 ligand as it is ammine. Therefore, name of the complex is [Co(H2O)4(NH3)2]Cl3 is Diamminetetraaqua cobalt (III) chloride.
Hence, the correct answer is (d).
Question 3: Two numbers are chosen from 1, 3, 5, 7, …… 147, 149 and 151 and multiplied together in all possible ways. The number of ways which will give us the product a multiple of 5, is:
(a) 75
(b) 1030
(c) 95
(d) 1020
Solution:
In the given numbers 1, 3, 5, 7, ..…, 147, 148, 151, the numbers which are multiple of 5 are 5, 15, 25, 35,…, 145 which are an arithmetic sequence. Below mentioned is the solution:
Hence, the correct answer is (d).
Question 4:
Solution:
Hence, the correct answer is (d).
Question 5: The image of an object, formed by a plano-convex lens at a distance of 8m behind the lens, is real and is one third the size of the object. The wavelength of light inside the lens is 2/3 times the wavelength in free space. The radius of the curved surface of the lens is
(a) 1 m
(b) 6 m
(c) 5 m
(d) 3 m
Solution:
Hence, the correct answer is (d).
Question 6: The resistance of a wire at room temperature 20°C is found to be 20W. Now to increase the resistance by 20%, the temperature of the wire must be [The temperature coefficient of resistance of the material of the wire is 0.002 per °C].
(a) 142°C
(b) 124°C
(c) 150°C
(d) 122°C
Solution:
Hence, the correct answer is (b).