The correct option is
A Splendour
A synonym is a word or a phrase that is similar in meaning to another word/phrase.
Option C: 'Glory' means 'magnificence or great beauty'.
'Splendour' means 'magnificent or splendid appearance, grandeur'.
Hence, 'splendour' and 'glory' mean the same, both refer to 'magnificence'.
Hence, option C is correct.
Option A: 'Beauty' means 'a combination of qualities, that pleases the aesthetic senses, especially the sight'. It does not mean the same as 'glory'. 'Glory' is a 'grand beauty', it refers to the grandiose of beauty. But, 'beauty' is not 'glory'.
Option B: 'Strength' means 'the quality or state of being physically strong'.
Option D: 'Popularity' means 'the state or condition of being liked or admired'.
These words do not mean the same as 'glory'. Hence, options A, B and D are wrong.