Which of the following is an example of a continuous emission spectrum in simple laboratory observations?

Introduction / Context:
In optics and atomic physics, spectra are classified into continuous, line and band spectra. A continuous emission spectrum shows an unbroken spread of wavelengths over a range, with all colours present without gaps. It is typically produced by hot solids, liquids or very dense gases. This question asks you to identify which of the listed examples is best associated with a continuous emission spectrum at a simple school-laboratory level.

Given Data / Assumptions:
- We are considering simple, qualitative observations rather than precise spectroscopic analysis.
- Option A refers to the spectrum of an oil flame, which includes glowing particles and heated gases.
- Option B refers to the spectrum of water, which by itself is not usually discussed as a light source.
- We interpret “spectrum of water” as not being a standard continuous emission source in basic physics.

Concept / Approach:
A continuous spectrum is produced when a hot solid, a hot liquid or a very dense gas emits light. Examples include the filament of an incandescent lamp, a metal rod heated until it glows, and luminous flames containing hot, dense particles. An oil flame, especially a yellow luminous flame, has glowing soot and hot gases and can approximate a continuous spectrum to the naked eye and simple spectroscopes. Water, on the other hand, is largely transparent and is not typically mentioned as an independent continuous emitter in school-level demonstrations. Therefore, the safest choice here is the oil flame spectrum.

Step-by-Step Solution:
Step 1: Recall that continuous spectra are associated with hot solids, liquids or dense gases emitting over a wide range of wavelengths. Step 2: Recognise that a luminous oil flame contains hot particles and dense gases and can produce a nearly continuous spectrum. Step 3: Consider water alone. It is not a standard example of a glowing body producing its own emission spectrum in basic experiments. Step 4: Option C claims both examples give continuous spectra, which is too broad and not supported in standard introductory texts. Step 5: Option D suggests that neither is an example, but that would ignore the approximate continuous nature of luminous flames. Step 6: Conclude that the most appropriate answer is the spectrum of an oil flame.

Verification / Alternative check:
In common school demonstrations, when students view the light from a candle or oil lamp through a simple spectroscope, they observe a broad, nearly continuous band of colours. This is often contrasted with the line spectra from gas discharge tubes. Water is not usually used as an emission source; instead, it may act as an absorbing or refracting medium. This supports choosing the oil flame as the better example of a continuous emission spectrum among the options given.

Why Other Options Are Wrong:
Spectrum of water: Water itself is not a typical luminous emitter in basic spectrum experiments, so this is not presented as a standard example of a continuous emission spectrum.
Both A and B: This overstates the case by including water as an emission source, which is not typical in introductory physics.
None of these: This ignores that luminous flames from oil or candles are widely treated as approximate continuous spectrum sources in simple observations.

Common Pitfalls:
Students sometimes expect only perfect blackbody sources like tungsten filaments to be called continuous and may forget that in practical, low-level experiments, luminous flames are accepted as approximate continuous emitters. Another source of confusion is taking vague options like “spectrum of water” at face value without thinking about whether water normally glows and emits on its own. Focusing on actual classroom and laboratory examples helps choose the most reasonable option.

Final Answer:
Among the options, the best example of a continuous emission spectrum is the spectrum of an oil flame.