Question

Among the following the correct statements are I. Neutrons are not deflected by any magnetic field. II. Cathode rays can be deflected by both magnetic and electric fields. III. Atomic weight of an element is not necessarily be a whole number because it is average isotopic weight. IV. The constancy of \(e / m\) ratio for electron shows that electron mass is \(1 / 1837\)th of proton. (1) I, II, III and IV (2) 1,11 and III (3) 1\(], 111\) and IV (4) \(1,11 \mid\) and IV

Short answer

Option (2) I, II, and III are correct.

Step-by-step solution

- Analyze Statement I

Neutrons are neutral particles and, therefore, do not carry any charge. Because magnetic fields exert a force on moving charged particles, neutrons are not affected by magnetic fields. Thus, statement I is correct.

- Analyze Statement II

Cathode rays consist of electrons, which are negatively charged particles. They can be deflected by both electric and magnetic fields. Thus, statement II is correct.

- Analyze Statement III

Atomic weight is the average mass of an element's isotopes, weighted by their natural abundance. Since isotopes have different masses, the atomic weight often is not a whole number. Thus, statement III is correct.

- Analyze Statement IV

The \(\frac{e}{m}\) ratio for electrons is a fundamental constant that doesn't directly show the electron's mass relative to the proton's mass. Instead, it is a measure of the charge-to-mass ratio. This statement is incorrect.

- Conclusion

Summarizing the analysis: Statements I, II, and III are correct, while statement IV is incorrect. Therefore, the correct answer is option (2) I, II, and III.

Key concepts

Neutron Properties

Neutrons are a fundamental part of the atomic structure, residing in the nucleus along with protons. They are neutral particles, meaning they carry no charge. This lack of charge means that neutrons are **not** deflected by magnetic fields. Magnetic fields exert forces only on charged particles, so the neutral neutrons pass through unaffected. Their neutrality also means they don’t interact with electric fields, further emphasizing their unique role in the atomic nucleus. This property makes neutrons especially important when studying atomic reactions and nuclear physics as they can penetrate dense materials better than charged particles.

Cathode Rays

Cathode rays are streams of electrons observed in vacuum tubes. These rays are produced when a high voltage is applied across a vacuum tube, causing electrons to move from the cathode (negative electrode) to the anode (positive electrode).
Electrons in the cathode rays carry a negative charge, allowing them to be deflected by magnetic and electric fields. This was crucial in early experiments, such as J.J. Thomson's, which helped to discover the electron. The deflection behavior of cathode rays under these fields provided significant insights into the nature of electrons and their properties.
Understanding cathode rays' behavior paved the way for modern electronic devices like televisions and computer screens, which rely on manipulating electron streams.

Atomic Weight

The atomic weight of an element is an averaged value that takes into account the different isotopes of that element and their relative abundances. Isotopes are atoms of the same element that have different numbers of neutrons, giving them different masses.
Because the atomic weight is an average of these isotopic masses, it is often not a whole number. For instance, chlorine has two main isotopes, Cl-35 and Cl-37. The atomic weight of chlorine is approximately 35.5, reflecting the weighted average of these two isotopes based on their natural abundance.
This concept is essential in chemistry and physics, affecting calculations in molecular mass, reaction stoichiometry, and material properties.

Charge-to-Mass Ratio

The charge-to-mass ratio \(\frac{e}{m}\) is a crucial concept in understanding the properties of subatomic particles like electrons. This ratio describes the amount of electrical charge an electron carries relative to its mass. For electrons, this ratio is quite large, reflecting their tiny mass compared to their charge.
In historical experiments, such as those conducted by J.J. Thomson, the charge-to-mass ratio was pivotal in identifying the electron as a distinct particle and understanding its very small mass relative to other subatomic particles like protons.
However, \(\frac{e}{m}\) for electrons doesn’t directly show how the electron's mass compares to the proton’s mass. Instead, it serves as a measure to understand electron behavior in electric and magnetic fields and has applications in mass spectrometry and other analytical techniques.