**1)**Why is ground state of carbon more stable than its excited state despite the fact that half-filled orbitals are more stable than fully-filled orbitals?

**2)**Two plano-concave lenses(A and B) of glass of refractive index 1.5 each have radii of curvature 25cm and 20cm.They are placed in contact with their curved surface towards each other and space between them is filled with liquid of refractive index 4/3.

Find the focal length of the combination.

**3)**A plano-convex lens fits exactly into a plano-concave lens.Their plane surfaces are parallel to each other.If the lenses are made of different materials of refractive indices \(a\) and \(b\) and radius of curvature \(R\),find the focal length of the combination.

**4)**What are some cool tricks to solve a network of resistors?

Like for example what should be our approach while solving a weird network of resistors for net resistance?

**5)**Why do d-block elements show great variations in their properties and why do they have variable oxidation state?

Please help me.Thanks!

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## Comments

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TopNewestAre you in class 12th ? Some of these would be clear if you have been taught about them .

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I am going to class 11.

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Can you please explain these to me? Thanks!

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@Rishabh Cool @Aditya Sharma @Aditya Kumar @Vighnesh Shenoy @Prakhar Bindal @Aniket Sanghi @Samarth Agarwal @(Everyone seeing this)

Sorry for mass tagging.

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Have patience till class 12 brother... or see any nice book of class 12. You will find each of them. Even NCERT would do for some. @Harsh Shrivastava

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Why should he have patience? There's are boundaries for acquiring knowledge.

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What I meant to say was just that before reading things which aren't in our syllabus at present and we know that we would be studying them in coming years, we should focus more on problem solving skills in topics we already know and then jump forward!

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Answer 1.

Existing carbon to higher level takes energy and this energy is then stored. Despite of having half filled configuration it has high energy which is unfavourable. Thus it releases energy and gets to ground state. Also, electrons change orbital only if it is lower on energy than the previous one.

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