A series of layers of the Sun is given with one term missing. Choose the correct alternative from the options that will complete the series. Core, Photosphere, Chromosphere, ?

Introduction / Context:
This question belongs to basic astronomy and general science. It lists several layers of the Sun, moving from the inner region towards the outer atmosphere. To fill the missing term, candidates must recall the usual order in which the major visible layers of the Sun are described. The series Core, Photosphere, Chromosphere suggests a progression outward, and we need to identify the next outer layer of the Sun's atmosphere that follows Chromosphere.

Given Data / Assumptions:

• Given series: Core, Photosphere, Chromosphere, ?
• The Core is the central region of the Sun where nuclear fusion occurs.
• The Photosphere is the visible surface layer of the Sun.
• The Chromosphere is a thin layer of the Sun's atmosphere above the Photosphere.
• We are looking for the next outer layer commonly listed after the Chromosphere.

Concept / Approach:
From inner to outer, the Sun is often described with the following major regions: core, radiative zone, convective zone, photosphere, chromosphere, and corona. In simplified descriptions that highlight visible atmospheric layers, the sequence usually mentions photosphere, chromosphere, and then corona. The given series has already moved from the core to photosphere and then to chromosphere, so the next natural term in this progression is the corona, which is the outermost part of the Sun's atmosphere visible during a total solar eclipse as a pearly white halo.

Step-by-Step Solution:
Step 1: Recall the main internal and external regions of the Sun: core (centre), radiative zone, convective zone, photosphere (visible surface), chromosphere, and corona (outer atmosphere). Step 2: Compare this full sequence with the one given in the question. The core represents the central region. The photosphere represents the visible surface just above the convective zone. The chromosphere lies just above the photosphere. Step 3: Identify the next distinct outer layer commonly named after the chromosphere. Standard descriptions always list the corona after the chromosphere. Step 4: Select Corona from the options as the correct term to complete the series Core, Photosphere, Chromosphere, Corona.

Verification / Alternative check:
To verify, we can think of how the Sun appears during a total solar eclipse. The photosphere is blocked, revealing the reddish chromosphere and, further out, the bright white corona. This visual order matches the scientific description of atmospheric layers. None of the other options matches a recognised solar layer after chromosphere; they are mostly associated with Earth or do not belong in this context. This supports corona as the only correct continuation of the given sequence.

Why Other Options Are Wrong:
Mantle, crust, and asthenosphere are layers associated with the Earth, not with the Sun. They describe parts of Earth's internal structure, such as Earth's mantle and crust, which have nothing to do with solar layers. The ionosphere is a region of Earth's upper atmosphere ionised by solar radiation, not a layer of the Sun itself. Therefore, none of these terms fits logically as the next layer of the Sun after chromosphere, whereas corona is the standard and correct term.

Common Pitfalls:
Students sometimes confuse layers of Earth with layers of the Sun because both are discussed in basic science. Choosing mantle or crust reflects this confusion. Others may pick ionosphere because it sounds related to space and charged particles, forgetting that it is an atmospheric layer of Earth, not of the Sun. A clear mental picture of the Sun's structure from core to corona helps avoid these mistakes in exam questions.

Final Answer:
The layer that follows Chromosphere in the outward sequence of the Sun's structure is the Corona.