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Q71. Which one of the following symmetry elements is an INCORRECT representation of rotoinversion operation?
The correct answer is 1A2 = 4̅. A 4-fold rotoinversion axis (4̅) actually implies a 2-fold rotation (1A2) in its overall symmetry, but stating they are exactly equal operations is incorrect because a 4̅ operation involves 90-degree rotations coupled with inversions, generating more complex symmetry points than a simple 180-degree 2-fold rotation (1A2). The other relationships correctly define standard rotoinversion equivalents, so they are not the incorrect representation we are looking for.
Q72. Which one of the following textures shows cuneiform-shape intergrowth between alkali feldspar and quartz?
The correct answer is Graphic texture. When alkali feldspar and quartz grow together at the same time from cooling magma, they can form a pattern that looks like ancient cuneiform writing, known as graphic texture. Spherulitic texture forms radiating needle-like crystals. Porphyritic texture features large crystals surrounded by very small ones. Spinifex texture is a criss-cross pattern of long olivine crystals, making all of these alternative options incorrect.
Q73. Which one of the following was emplaced in the Neoproterozoic time?
The correct answer is Erinpura Granite. The Neoproterozoic is a specific era of geological time (roughly 1 billion to 538 million years ago). In Indian geology, the Erinpura Granite formed during this time period. The Singhbhum, Dongargarh, and Closepet Granites are all much older, having formed during the Archean Eon or early Proterozoic, making them incorrect.
Q74. A horizontal upright fold will have a
The correct answer is horizontal fold axis and vertical axial plane. Imagine taking a flat rug and pushing the sides together so it forms an arch. If the arch stands straight up, the imaginary wall cutting it perfectly in half (the axial plane) is 'vertical' (upright). The top ridge of the arch (the fold axis) runs perfectly flat along the ground, meaning it is 'horizontal'. This geometry rules out vertical axes or slanted (plunging/dipping) planes.
Q75. An index fossil should have
The correct answer is large geographic range and small temporal range. An 'index fossil' is the perfect geological stopwatch used to date rocks. To be useful, the creature must have quickly spread all across the globe so it can be found in rocks anywhere ('large geographic range'). But, it must have also gone extinct very quickly, so its fossil only appears in one very thin, specific time layer of rock ('small temporal range'). All other options make the fossil too localized or too long-living to be a precise global time marker.
Q76. Buckle folds result from
The correct answer is layer parallel shortening. Imagine holding a piece of paper flat on a table and pushing the left and right edges directly toward each other. The paper buckles upward into an arch. In geology, this side-to-side pushing that runs parallel to the flat rock layer is called 'layer parallel shortening', and it causes the rock to wrinkle into 'buckle folds'. The other options describe sliding or squashing from top-to-bottom, which do not create these specific buckling arches.
Q77. In the holosymmetric class of the Cubic System, how many more faces does the {110} form have compared to the {111} form?
The correct answer is 4. Crystals are described by the shapes of their faces. In a perfectly symmetric cubic crystal, the {111} form creates an octahedron, which has 8 faces (like two pyramids stuck base-to-base). The {110} form creates a rhombic dodecahedron, which has 12 faces. Taking the difference between them (12 minus 8) leaves exactly 4 more faces. Thus, the other numerical options are mathematically incorrect.
Q78. Increased diversity of siphonate bivalves occurred in response to
The correct answer is increased predation pressure in the Mesozoic. 'Siphonate bivalves' are clams equipped with fleshy tubes (siphons) that act like snorkels, allowing them to bury deep under the sand to hide while still breathing. During the Mesozoic era, new sea predators like advanced crabs and fish evolved to crack open shells. To survive this 'predation pressure', clams rapidly evolved siphons to hide deep underground. The other time periods and causes do not match this evolutionary arms race.
Q79. Realgar and orpiment are both minerals of arsenic (As) and have the same chemical composition. Which one of the following properties can be used to distinguish between the two minerals in hand specimen?
The correct answer is Colour. Realgar and orpiment are famous arsenic minerals that often grow together. The easiest and most reliable way for anyone to tell them apart just by looking at them is their vivid color: Realgar is a deep, fiery ruby-red, while Orpiment is a bright, vibrant lemon-yellow. Their lustre, hardness, and fracture are very similar, making those properties unhelpful for quick visual identification.
Q80. Sandstone beds above a magmatic body are domal in shape, while the beds below are horizontal. The magmatic body is a
The correct answer is Laccolith. When liquid magma forces its way between flat layers of underground rock, it can pump up like a thick blister, pushing the rock layers above it into a dome shape while the floor beneath it remains perfectly flat. This specific mushroom-shaped blister is called a Laccolith. A sill is flat on both the top and bottom. A lopolith sags downward like a bowl. A batholith is an unimaginably massive, irregular magma chamber, making the other options wrong.