Questions & Answers about Они скоро объявят платформу.
Why is there a hard sign (ъ) in объявят?
The hard sign (ъ) separates a prefix ending in a consonant (об-) from a root starting with a soft, iotated vowel like я, е, ё, or ю. It stops the consonant from blending into the vowel, meaning you pronounce a distinct Y-sound right after the prefix.
Why does this verb translate to the future tense instead of the present?
объявят is a perfective verb. In Russian, perfective verbs do not have a present tense. When you conjugate them using the standard present-tense endings, the meaning is always future.
What is the imperfective pair for this verb, and how do their conjugations differ?
The imperfective is объявлять. A tricky detail is that they belong to different conjugation groups. The perfective объявить uses second conjugation endings (они объявят), but the imperfective объявлять uses first conjugation endings (они объявляют).
How does this sentence fit into a lesson about trains departing?
While this specific sentence does not use a verb of motion, it is a very common phrase to hear at a Russian train station. You usually wait until they announce the platform (объявят платформу) before you go to your train and wait for it to depart (отойти).