"Is it near?"
In general, you use 近い as the adjective form by itself or talking about the nearness of something
The station is nearby - 駅は近いです
You'll use the adverb form 近く when talking about the nearness in relationship to another object. You usually see it as OBJECTの近く:
The cat is near the bag - 猫は鞄の近くです
But in the case of 猫は鞄の近くです, isn't -の近く functioning as a preposition (or a postposition, as it were), just like -の上, -の間, etc., rather than an adverb? Or am I wrong?
I believe you make it -く and add ない when you want to make it negative. Otherwise you just leave it -い
ちかい means close ちかくない means not close
I think most adjectives ending in -い change like this.
the past tense of い adjectives is formed by taking out the trailing い and adding かった, as you'll see in later lessons. you then have 近かった (ちかかった) meaning "was near", and 「近かったですか」 would be "was it near?"