The question asks to identify a physical change among the given options. A physical change is a type of change in which the form of matter is altered but not its chemical identity. No new substances are formed, and the change is often reversible. Chemical changes, on the other hand, result in the formation of new substances with different chemical properties.
Correct Option: D) Dissolution of sugar in water is a physical change because the chemical composition of sugar does not change; it merely disperses in water, and can be recovered by evaporating the water.
The question asks for the causative agent of cholera. This requires knowledge of common infectious diseases and their microbial origins.
Correct Option: A) Cholera is an acute diarrheal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae. This bacterium produces a toxin that causes severe watery diarrhea, leading to dehydration and, if untreated, can be fatal.
The question asks to identify an apparatus used for viewing objects above eye level when direct vision is obstructed. We need to evaluate each option based on its function.
Correct Option: B) A Periscope is an optical instrument that allows an observer to see objects that are otherwise obstructed from direct view, often by using mirrors or prisms to reflect light. This is precisely what is described in the question.
To determine which atom has only one electron, we need to recall the atomic number of each element listed in the options. The atomic number (Z) of an element represents the number of protons in its nucleus, and for a neutral atom, it also equals the number of electrons.
D) Hydrogen. A neutral hydrogen atom (H) has an atomic number of 1, meaning it has 1 proton and 1 electron.
The question asks to identify the organic acid present in vinegar. This is a direct knowledge-based question related to common chemical compounds and their sources.
Therefore, the organic acid present in vinegar is ethanoic acid.
D) ethanoic acid — Vinegar is a dilute solution of acetic acid, which is systematically named ethanoic acid. Its chemical formula is \( \text{CH}_3\text{COOH} \).
The question asks about the composition of "water gas." This is a common term in industrial chemistry and fuel technology. We need to recall the chemical components that make up water gas.
A) a mixture of carbon monoxide and hydrogen — This correctly identifies the primary components of water gas, as produced by the reaction of steam with hot carbon.
The problem asks for the magnitude of the change in velocity of a body that strikes a floor vertically and rebounds. Velocity is a vector quantity, meaning it has both magnitude and direction. When a body rebounds, its direction of motion reverses, while its speed (magnitude of velocity) remains the same as given in the problem.
D) 2u is the correct answer. The change in velocity is \(2u\) because the direction of velocity reverses while its magnitude remains the same.
This question asks us to identify the odd one out from a list of physical quantities. The key to solving this is to classify each quantity as either a scalar or a vector.
D) Force is a vector quantity, meaning it has both magnitude and direction. The other options (Speed, Time, Density) are scalar quantities, possessing only magnitude.
To find the momentum of an object, we use the fundamental formula for momentum, which is the product of its mass and velocity. We are given the mass of the man and his uniform velocity, so we can directly apply this formula.
Momentum (\(p\)) is defined as the product of mass (\(m\)) and velocity (\(v\)).
\[ p = m \times v \]D) 150 kg m/s — The calculation \(75 \text{ kg} \times 2 \text{ m/s} = 150 \text{ kg m/s}\) correctly yields the momentum.
The acceleration due to gravity, \(g\), varies with depth below the Earth's surface. We need to determine its value at the Earth's center using the relevant formula for gravitational acceleration inside a uniform sphere.
The acceleration due to gravity (\(g\)) at a depth \(d\) below the Earth's surface is given by the formula:
\[ g_d = g \left(1 - \frac{d}{R}\right) \]where:
At the center of the Earth, the depth \(d\) is equal to the radius of the Earth, i.e., \(d = R\).
Substitute \(d = R\) into the formula:
\[ g_{\text{center}} = g \left(1 - \frac{R}{R}\right) \]Simplify the expression:
\[ g_{\text{center}} = g (1 - 1) \]\[ g_{\text{center}} = g (0) \]\[ g_{\text{center}} = 0 \]Thus, the value of acceleration due to gravity at the center of the Earth is zero.
C) zero — As derived, at the center of the Earth, the depth \(d\) equals the radius \(R\), making the term \((1 - d/R)\) equal to zero, and consequently, \(g_{\text{center}} = 0\).