Atomic Structure and Mass

The elements of the triads had similar properties and when arranged in the increasing order of atomic masses, the atomic mass of the middle element was roughly the arithmetic mean of the masses of the other two elements.

Here, the ratio of number of neutrons to that of protons is greater than 1, which means that it is an unstable element. Hence, it is a radioisotope of cobalt.

This is the correct answer as protons and neutrons determine the mass of an element.

This is the correct answer as isotopes are atoms of the same element.

The chemical identity of an element is determined solely by its number of protons (atomic number). Changing the number of neutrons creates isotopes of the same element, while changing electrons creates ions. Only altering the proton count changes which element it is.

Newlands, Mendeleev and Dobereiner all tried to correlate the properties of elements with their atomic masses. Newlands, an English scientist, arranged the elements in order of their increasing atomic masses. He started with hydrogen (atomic mass 1 u), the element having the lowest atomic mass and ended with thorium, which was the 56^th element. He found that the properties of the eighth element were similar to the properties of the first element. Dobereiner tried to arrange the elements with similar properties into groups called triads having 3 elements each. According to Dobereiner, when the elements of any particular triad were arranged in order of their increasing atomic masses, the atomic mass of middle element was roughly the mean or average of the atomic masses of the other two elements. Mendeleev, in his periodic table, classified the elements on the basis of their increasing atomic masses and the formula of their oxides and hydrides. Later on, Henry Moseley discovered that atomic number is a more appropriate parameter to determine the properties of an element rather than its atomic mass.

A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings. The concept is important in nuclear weapon design.

This answer is correct as when H₂O is ionised by the bombardment of electron beam it can get converted to H⁺, O⁺, [OH]⁺, [H₂O] having masses 1, 16, 17 and 18 respectively. But none of these configurations give mass of 15. Hence, there can be no peak corresponding to  mass 15.

The atomic mass unit (amu or unified atomic mass unit, u) is defined as exactly 1/12 the mass of a neutral carbon-12 atom in its ground state. This standard was chosen because carbon-12 has six protons and six neutrons, making calculations convenient. The value is approximately 1.660539 x 10^-27 kg. Options B and C reference oxygen and hydrogen which were older standards.

Here, the ratio of number of neutrons to that of protons is greater than 1. Hence, it is a radioisotope of cobalt.

The number of neutrons in an atom is calculated by subtracting the atomic number (number of protons) from the mass number (total nucleons). For this element: Neutrons = Mass number - Atomic number = 226 - 88 = 138. This element is Radium-226.

This is the correct answer. The combining capacity of an element is called its valency.

Atomic mass of zinc = 65.37 u 1u = 1.67 x 10^-24 g. Atomic mass of zinc = 65.37 u = 65.37 x 1.67 x 10^-24 = 1.09 x 10^-22 g

This is the correct answer as both these statements are correct.

The atomic number of carbon is 6, which means it has 6 protons in its nucleus. This also means it has 6 electrons in a neutral atom, arranged as 2,4 in electron shells (K and L shells).